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Main
Date: 02 May 2007 21:21:44
From: Bullseye
Subject: 4 inch reflector can't resolve Mars at all
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I have a Nexstar 114GT and it can give visuals of the moon nicely
(most scopes can I think) but I can't see sqwat when I point to Mars.
I pointed to it 1-2 years ago when it was all over the news that it
was close to Earth, but all I could see was a pink little ball, no
features at all. Also in Saturn all I could see is a tiny little dot
with a tiny circle around it. I've centered the scope and adjusted it
all the ways I'm supposed to to get the best image (I've forgotten the
exact terms that are used since I've ditched astronomy for awhile),
but trust me I did. I just want to sell this sucker and get a new one.
Can anyone recommend the best 4 inch reflectors out there for less
than $500? Or maybe a very good 8 inch dob for less than $500?
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Date: 11 May 2007 17:11:42
From:
Subject: Re: 4 inch reflector can't resolve Mars at all
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On May 11, 1:26 pm, "b...@ei.com" <Bullseye > wrote:
> On Thu, 10 May 2007 05:23:55 GMT, Jim Klein
>
> <jamesekl...@earthlink.net> wrote:
> >A good 8" or larger aperture Newtonian is the key. F/8 or greater.
>
> The Orion XT8 is an f/6 scope, are you saying this isn't a good enough
> scope? I looked at the Discovery telescopes site but that's an f/7,
> and it costs $999! I thought it was supposed to be about the same as
> the Orion. Anyway what 8" dob can you recommend?
Helpful hints:
An 8 f/6 will fit into the back seat of most cars. For an f/8 you
might need a minivan.
8" f/8 mirrors seem to be custom orders these days.
An 8" f/8 could, potentially, be a little bit better than an 8" f/6,
but either one is much better than a 4-inch.
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Date: 10 May 2007 03:20:20
From:
Subject: Re: 4 inch reflector can't resolve Mars at all
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On May 10, 1:23 am, Jim Klein <jamesekl...@earthlink.net > wrote:
> Bullseye <b...@ei.com> wrote:
> >I have a Nexstar 114GT and it can give visuals of the moon nicely
> >(most scopes can I think) but I can't see sqwat when I point to Mars.
> >I pointed to it 1-2 years ago when it was all over the news that it
> >was close to Earth, but all I could see was a pink little ball, no
> >features at all. Also in Saturn all I could see is a tiny little dot
> >with a tiny circle around it. I've centered the scope and adjusted it
> >all the ways I'm supposed to to get the best image (I've forgotten the
> >exact terms that are used since I've ditched astronomy for awhile),
> >but trust me I did. I just want to sell this sucker and get a new one.
> >Can anyone recommend the best 4 inch reflectors out there for less
> >than $500? Or maybe a very good 8 inch dob for less than $500?
>
> A good 8" or larger aperture Newtonian is the key. F/8 or greater.
>
> You need good seeing, a clock drive and at least 1/20 wave peak to
> valley quality in the mirror and diagonal.
>
> I've seen more in a good 8" than an average 10". High optical quality
> is the key.
>
> The eye has a resolution of about 1 min of arc. A 10" has a resolution
> of about 0.015 min of arc. Thus you will need about 100 to 200 power
> to see as much as a 10" telescope can resolve (at best). Experience
> shows that 50x per inch is about the max usable which in the case of
> a 10" yields 500x.
>
> A 1/20 wave optical train 10" with perfect seeing and 500x ought to
> put you in Mars heaven without requiring a Lottery win.
>
> 10" f/8 would need an eyepiece of about 1/4 inch or 6 mm to get to
> 500x. Use a good plossel or an achromat.
>
> More aperture is always better as long as the seeing will support it.
> Remember, the telescope magnifes the seeing as well as the object
> being observed.
>
What can you recommend in the < $500 price range?
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Date: 10 May 2007 03:17:25
From:
Subject: Re: 4 inch reflector can't resolve Mars at all
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On May 9, 12:20 am, David Knisely <KA0...@navix.net > wrote:
> wsnell01 wrote:
> > What you were actually doing earlier was dismissing coma as a problem
> > (so far, so good) by replacing it with astigmatism as a problem, when
> > in fact neither is a problem big enough to worry about, especially
> > when you consider all of the other factors.
>
> No, again, you are missing the point. Any f/6 scope will make some of
> the less corrected eyepiece designs generate visible astigmatism near
> the outer edge of the field. It is a problem which in many cases is
> larger than that of the coma produced by an 8 inch f/6 paraboloid. The
> coma is small, small enough that the off-axis astigmatism shown with
> many eyepieces is enough to obscure it to a large extent. The
> astigmatism isn't "replacing" anything. It is an eyepiece-related
> problem with f/6 light cones and many of the more common bargain
> eyepiece designs, period. There were not any other factors mentioned,
> nor were they needed, as that was *not* the point of discussion.
No, you are missing the point, i.e., coma and astigmatism, in this
case, are such minor considerations that it doesn't even matter which
is worse.
Here is how a newbie might interpret this subthread:
USENET User 1: "Dobsonians don't track and at high power it's hard to
keep an object dead-center in the field of view, and if you don't,
coma will ruin the image."
USENET User 2: "That's not coma, that's astigmatism. I had to use a $
$$ eyepiece to get rid of the astigmatism, so that I could even see
the coma."
USENET Lurker/Newbie thinks to himself: "Wow, Dobsonians have so many
problems. No wonder they don't cost much. Maybe I should try
something else. Maybe this hobby is too expensive."
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Date: 10 May 2007 13:20:31
From: Chris L Peterson
Subject: Re: 4 inch reflector can't resolve Mars at all
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On 10 May 2007 03:17:25 -0700, wsnell01@hotmail.com wrote:
>Here is how a newbie might interpret this subthread:
>
>USENET User 1: "Dobsonians don't track and at high power it's hard to
>keep an object dead-center in the field of view, and if you don't,
>coma will ruin the image."
>
>USENET User 2: "That's not coma, that's astigmatism. I had to use a $
>$$ eyepiece to get rid of the astigmatism, so that I could even see
>the coma."
>
>USENET Lurker/Newbie thinks to himself: "Wow, Dobsonians have so many
>problems. No wonder they don't cost much. Maybe I should try
>something else. Maybe this hobby is too expensive."
Well, here's how a newbie _should_ interpret things:
If I'm interested in critical, high power observation of planets, I need
to be aware that a Dob doesn't track, and keeping the planet in the
center of the field requires some effort. That may be more effort than
I'd like to spend, and may indeed interfere with my ability to observe.
I should consider evaluating a Dob for planetary observation before
purchasing one.
I should also be aware that typical uncorrected Newtonians display
several off-axis aberrations, and while these are usually considered
fairly minor, they are significant enough to visibly degrade planetary
images as the target leaves the center of the field.
Nothing here says that a newbie shouldn't buy a Dob, or that they have
lots of problems. It only says that (like all scopes) they have
limitations that should be considered by a potential purchaser, and that
those limitations happen to be a little more obvious to planetary
observers than to deep sky observers.
_________________________________________________
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com
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Date: 10 May 2007 12:02:35
From: Dennis Woos
Subject: Re: 4 inch reflector can't resolve Mars at all
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> I should also be aware that typical uncorrected Newtonians display
> several off-axis aberrations, and while these are usually considered
> fairly minor, they are significant enough to visibly degrade planetary
> images as the target leaves the center of the field.
>
I don't think you ever confirmed that the amount of coma and astigmatism
exceeded the size of the Airy disk for an f/6 Newtonian and a typical
high-power eyepiece?
Dennis
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Date: 10 May 2007 21:36:07
From: Chris L Peterson
Subject: Re: 4 inch reflector can't resolve Mars at all
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On Thu, 10 May 2007 12:02:35 -0400, "Dennis Woos" <dpwoos@gmavt.net >
wrote:
>I don't think you ever confirmed that the amount of coma and astigmatism
>exceeded the size of the Airy disk for an f/6 Newtonian and a typical
>high-power eyepiece?
With an f/6 parabolic mirror, the coma is outside the Airy disk at about
10 Jupiter diameters, which is well inside the FOV of many high power
eyepieces. More to the point, however, is the effect on the MTF, which
is significant even when the coma is entirely inside the Airy disk
(which is why using the Airy disk as a criterion isn't very valid). Only
3 Jupiter diameters from the center, the mid-range MTF has dropped over
10%, which is more than the drop going from an unobstructed to a 30%
obstructed design. Many critical observers would consider this drop in
contrast to be significant. And this is without considering the eyepiece
at all.
I've never observed planets at high power in any type of scope, with any
type of eyepiece, where I couldn't readily see a loss of planetary
detail away from the center. I'm sure part of that has to do with
eyepiece aberrations, and part to do with coma, astigmatism, or field
curvature, depending on the type of scope. I can't imagine anybody
trying to get maximum detail when viewing a planet letting that planet
get very far from the center of the field.
Going back to the original advice I gave that started all this, the
point wasn't that there's a problem with Newts as such (virtually all
scope designs have off-axis aberrations), but that people with a primary
interest in planetary observing might want to seriously consider the
added value that a tracking mount delivers.
_________________________________________________
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com
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Date: 10 May 2007 05:23:55
From: Jim Klein
Subject: Re: 4 inch reflector can't resolve Mars at all
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Bullseye <bulls@ei.com > wrote:
>I have a Nexstar 114GT and it can give visuals of the moon nicely
>(most scopes can I think) but I can't see sqwat when I point to Mars.
>I pointed to it 1-2 years ago when it was all over the news that it
>was close to Earth, but all I could see was a pink little ball, no
>features at all. Also in Saturn all I could see is a tiny little dot
>with a tiny circle around it. I've centered the scope and adjusted it
>all the ways I'm supposed to to get the best image (I've forgotten the
>exact terms that are used since I've ditched astronomy for awhile),
>but trust me I did. I just want to sell this sucker and get a new one.
>Can anyone recommend the best 4 inch reflectors out there for less
>than $500? Or maybe a very good 8 inch dob for less than $500?
A good 8" or larger aperture Newtonian is the key. F/8 or greater.
You need good seeing, a clock drive and at least 1/20 wave peak to
valley quality in the mirror and diagonal.
I've seen more in a good 8" than an average 10". High optical quality
is the key.
The eye has a resolution of about 1 min of arc. A 10" has a resolution
of about 0.015 min of arc. Thus you will need about 100 to 200 power
to see as much as a 10" telescope can resolve (at best). Experience
shows that 50x per inch is about the max usable which in the case of
a 10" yields 500x.
A 1/20 wave optical train 10" with perfect seeing and 500x ought to
put you in Mars heaven without requiring a Lottery win.
10" f/8 would need an eyepiece of about 1/4 inch or 6 mm to get to
500x. Use a good plossel or an achromat.
More aperture is always better as long as the seeing will support it.
Remember, the telescope magnifes the seeing as well as the object
being observed.
Jim Klein
James E. Klein
jameseklein@earthlink.net
Engineering Calculations
http://www.ecalculations.com
ecalculations@ecalculations.com
Engineering Calculations is the home of
the KDP-2 Optical Design Program
for Windows.
1-818-507-5706 (Voice and Fax)
1-818-823-4121
"KDP2, not quite easy enough for a Caveman to use" :-)
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Date: 11 May 2007 17:26:45
From: bulls@ei.com
Subject: Re: 4 inch reflector can't resolve Mars at all
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On Thu, 10 May 2007 05:23:55 GMT, Jim Klein
<jameseklein@earthlink.net > wrote:
>A good 8" or larger aperture Newtonian is the key. F/8 or greater.
The Orion XT8 is an f/6 scope, are you saying this isn't a good enough
scope? I looked at the Discovery telescopes site but that's an f/7,
and it costs $999! I thought it was supposed to be about the same as
the Orion. Anyway what 8" dob can you recommend?
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Date: 11 May 2007 18:10:07
From: Chris L Peterson
Subject: Re: 4 inch reflector can't resolve Mars at all
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On Fri, 11 May 2007 17:26:45 GMT, "bulls@ei.com" <Bullseye > wrote:
>The Orion XT8 is an f/6 scope, are you saying this isn't a good enough
>scope?
Not at all- this is a fine scope (focal ratio isn't really a very
important consideration with telescopes, except when talking about very
short focal ratios).
_________________________________________________
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com
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Date: 11 May 2007 13:59:32
From: Dennis Woos
Subject: Re: 4 inch reflector can't resolve Mars at all
|
>
>>A good 8" or larger aperture Newtonian is the key. F/8 or greater.
>
> The Orion XT8 is an f/6 scope, are you saying this isn't a good enough
> scope? I looked at the Discovery telescopes site but that's an f/7,
> and it costs $999! I thought it was supposed to be about the same as
> the Orion. Anyway what 8" dob can you recommend?
This is the problem with this thread - you are lead to believe that an 8"
f/6 scope isn't very good. This is crap. The issues (if there are any) are
so minor as to be pointless in this discussion. You need to seek out your
local astro club and check out some scopes in action. I believe that you
will find that a 8" f/6 dob provides views that will simply amaze you.
Don't believe me (or anyone else) - go and look for yourself and learn from
other local enthusiasts.
Dennis
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Date: 12 May 2007 00:07:55
From: bulls@ei.com
Subject: Re: 4 inch reflector can't resolve Mars at all
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On Fri, 11 May 2007 13:59:32 -0400, "Dennis Woos" <dpwoos@gmavt.net >
wrote:
>>
>>>A good 8" or larger aperture Newtonian is the key. F/8 or greater.
>>
>> The Orion XT8 is an f/6 scope, are you saying this isn't a good enough
>> scope? I looked at the Discovery telescopes site but that's an f/7,
>> and it costs $999! I thought it was supposed to be about the same as
>> the Orion. Anyway what 8" dob can you recommend?
>
>This is the problem with this thread - you are lead to believe that an 8"
>f/6 scope isn't very good. This is crap. The issues (if there are any) are
>so minor as to be pointless in this discussion. You need to seek out your
>local astro club and check out some scopes in action. I believe that you
>will find that a 8" f/6 dob provides views that will simply amaze you.
>Don't believe me (or anyone else) - go and look for yourself and learn from
>other local enthusiasts.
>
>Dennis
>
Not to mention I don't think there are any 8 inch f/8 dobs, or if
there are they are rare. The only f/8 I've seen was a 6 inch because
it's smaller. The Discovery is f/7, but also $999. I've heard a lot of
good stuff about the Orion XT8 so I think it is good enough.
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Date: 11 May 2007 23:51:59
From: Dennis Woos
Subject: Re: 4 inch reflector can't resolve Mars at all
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> Not to mention I don't think there are any 8 inch f/8 dobs, or if
> there are they are rare. The only f/8 I've seen was a 6 inch because
> it's smaller. The Discovery is f/7, but also $999. I've heard a lot of
> good stuff about the Orion XT8 so I think it is good enough.
A guy in our club has the Orion XT8, and here is the scoop on his scope. It
provides very good views, everyone in the club enjoys looking through it,
and it is one of the better 8" scopes in our club. It does not star test as
a super high quality optic, but it is certainly at least 1/4 wave, and the
good views support this. The rack-and-pinion focuser is satisfactory; it is
not a high-end unit but it is certainly not junk. The movement of the scope
was not great, and the owner eventually rebuilt the azimuth bearing with
Ebony Star and Teflon. This was the worse aspect of the scope, but even
this was not a show-stopper and the guy used the scope for something like a
year before he upgraded it. The upgrade was not a big deal, and he and I
did it in a couple of hours.
Of course, this is just one example and not a very current one. However,
there is no reason to believe that the current models aren't at least as
good. I don't think you will be disappointed, but if you are you can return
it as Orion's customer service is excellent. If you are rich then you
should buy a better scope - both optically and mechanically. You can also
build a better scope if you are into that sort of thing, which is what my
sons and I like to do. But if the XT8 fits your budget and interests then I
think it should be most satisfactory.
Dennis
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Date: 12 May 2007 19:02:47
From: Invalid
Subject: Re: 4 inch reflector can't resolve Mars at all
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Dennis Woos wrote:
>The movement of the scope was not great, and the owner eventually
>rebuilt the azimuth bearing with Ebony Star and Teflon.
What is "Ebony Star?"
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Date: 12 May 2007 16:38:50
From: Dennis Woos
Subject: Re: 4 inch reflector can't resolve Mars at all
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>
>>The movement of the scope was not great, and the owner eventually
>>rebuilt the azimuth bearing with Ebony Star and Teflon.
>
> What is "Ebony Star?"
>
Wilsonart's Ebony Star is a laminate that, when paired with Teflon and
loaded at 15psi, is the number one bearing material for small/medium dobs.
In fact, I think that any laminate with a bumpy surface probably works as
well.
Dennis
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Date: 12 May 2007 08:45:11
From: bulls@ei.com
Subject: Re: 4 inch reflector can't resolve Mars at all
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On Fri, 11 May 2007 23:51:59 -0400, "Dennis Woos" <dpwoos@gmavt.net >
wrote:
>A guy in our club has the Orion XT8, and here is the scoop on his scope. It
>provides very good views, everyone in the club enjoys looking through it,
>and it is one of the better 8" scopes in our club. It does not star test as
>a super high quality optic, but it is certainly at least 1/4 wave, and the
>good views support this. The rack-and-pinion focuser is satisfactory; it is
>not a high-end unit but it is certainly not junk. The movement of the scope
>was not great, and the owner eventually rebuilt the azimuth bearing with
>Ebony Star and Teflon. This was the worse aspect of the scope, but even
>this was not a show-stopper and the guy used the scope for something like a
>year before he upgraded it. The upgrade was not a big deal, and he and I
>did it in a couple of hours.
>
>Of course, this is just one example and not a very current one. However,
>there is no reason to believe that the current models aren't at least as
>good. I don't think you will be disappointed, but if you are you can return
>it as Orion's customer service is excellent. If you are rich then you
>should buy a better scope - both optically and mechanically. You can also
>build a better scope if you are into that sort of thing, which is what my
>sons and I like to do. But if the XT8 fits your budget and interests then I
>think it should be most satisfactory.
>
>Dennis
If I were rich I wouldn't be talking about an 8 incher, I'd be talking
about a 20-40 incher :) Thanks for the review.
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Date: 12 May 2007 07:04:57
From: Dennis Woos
Subject: Re: 4 inch reflector can't resolve Mars at all
|
> If I were rich I wouldn't be talking about an 8 incher, I'd be talking
> about a 20-40 incher :) Thanks for the review.
Maybe you would and maybe I would, but the most expensive scope owned by a
member of our club is a 6" AstroPhysics refractor and mount. Who knows,
depending on how your interests develop you may find yourself desiring less
aperture rather than more!
If you get the XT8, don't forget to think about collimation. There are many
tools which will enable you to achieve excellent collimation. I personally
like the barlowed laser method, and trust my Glatter laser collimator
coupled with an inexpensive barlow. Google "barlow laser collimation" and
"newtonian collimation" for lots of info on different methods. If you
decide to go the laser route, don't be too cheap as a misaligned laser will
result in misaligned optics. A good collimation tool is like a good
eyepiece - it will serve you for a lifetime. Finally, there is no reason to
struggle with collimation, and if you find that you are then you should
definitely seek the assistance of your local astro club, where you will find
someone who can show you how to do it in a few minutes.
Dennis
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Date: 11 May 2007 21:08:42
From: Starlord
Subject: Re: 4 inch reflector can't resolve Mars at all
|
My Scope that I named Babylon 8 IS a 8inch F8 scope, in another month it
should be back together and I'll be viewing with it again.
--
Telescope Buyers FAQ
http://home.inreach.com/starlord
Sidewalk Astronomy
www.sidewalkastronomy.info
"Dennis Woos" <dpwoos@gmavt.net > wrote in message
news:134aef4hol7es16@corp.supernews.com...
>> Not to mention I don't think there are any 8 inch f/8 dobs, or if
>> there are they are rare. The only f/8 I've seen was a 6 inch because
>> it's smaller.
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Date: 12 May 2007 02:22:35
From: Borked Pseudo Mailed
Subject: Re: Shitetards 4 inch arsehole can't buggars at awl
|
spammertard <starlord@sidewalkastronomy.info > feltched a bugger:
>My bell end Scope that i nam babelshite 8 arse a 2inch twaddle scoop in another mouth it
>shuodb ed nutsack shela bugger my arsehole to get her and i am men to lilly
>beleviewing with nancy nut my arsehole is sore
>
> the festering pustule on my sphincter is inflaming faggotard fawk i hurts
>i need to oil up my wagon for the bugger star pizza party up my shitey arsehole
> my wagon is red me ickle radio flyer i hobble up to the local off licence
>with my wagon in tow i named my wagon rosebugger it squeaks along 20th st
>
> squeak squeak squeak squeak hobble hicup squeak squeak
>guzzle guzzle brrrrrraaaaaaaaaaaappppppppppppppp
>
> i am shitetard my name is dennis bishop the nancytard of rosatard
>
>i arm mulatto he stalkertard of ghettotard nappy headed ho harvey buggers my wagon
> my poofter park manager gives me the reach around ooh aah rrraaaaaahhhhhh
>
> he is my bugger sod i swallow when he tells me to he knocks off a few quid on my
>rent in front of children please nurse my ninnie tips my nancy teats
>
> i wear a b cup
>
oh dennis you bugger boy let us wax up our telescopes and investigate uranus
>
>
>
>
>"Dennis Woos" <dpwoos@gmavt.net> wrote in message
>news:134aef4hol7es16@corp.supernews.com...
>>> Not to mention I don't think there are any 8 inch f/8 dobs, or if
>>> there are they are rare. The only f/8 I've seen was a 6 inch because
>>> it's smaller.
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Date: 09 May 2007 22:32:52
From: Brian Tung
Subject: Re: 4 inch reflector can't resolve Mars at all
|
Jim Klein wrote:
> You need good seeing, a clock drive and at least 1/20 wave peak to
> valley quality in the mirror and diagonal.
Good seeing is a must, a clock drive is definitely useful, but 1/20-wave
P-V is overkill. Most of the time, even good seeing will swamp that
kind of surface error. And 1/20-wave P-V is pretty hard to obtain on a
medium-to-large mirror.
> I've seen more in a good 8" than an average 10". High optical quality
> is the key.
The two inches are probably worth about 1/8-wave worth of SA. Just to
put a price on that optical perfection. :)
> The eye has a resolution of about 1 min of arc. A 10" has a resolution
> of about 0.015 min of arc. Thus you will need about 100 to 200 power
> to see as much as a 10" telescope can resolve (at best).
By nighttime, the eye generally has worse resolution than 1 arcminute
(and that's pretty darned good--most people are worse during the day,
too). That is why higher magnification is still useful for observers--
because the visible detail is still limited by the resolution of the
eye, not by the quality of the image.
For instance, most people have trouble splitting the Double Double
(about 3.5 arcminutes) with the unaided eye. I don't, but my visual
resolution is pretty good (for now!). A resolution of 3.5 arcminutes
works out to about 40x or 50x per inch--the typical rule of thumb.
> 10" f/8 would need an eyepiece of about 1/4 inch or 6 mm to get to
> 500x. Use a good plossel or an achromat.
A 10-inch f/8 needs more like 4 mm to get 500x: 80 inches is about 2000
mm. Plossls are good; what do you mean by achromat--like the Modified
Achromat or SMAs that Celestron used to sell a while back? Those are
basically Kellners, I think, and work OK at f/8, but I'd prefer a
Plossl to them. Also, I don't think they're commonly packaged with the
Celestrons and Meades anymore.
--
Brian Tung <brian@isi.edu >
The Astronomy Corner at http://astro.isi.edu/
Unofficial C5+ Home Page at http://astro.isi.edu/c5plus/
The PleiadAtlas Home Page at http://astro.isi.edu/pleiadatlas/
My Own Personal FAQ (SAA) at http://astro.isi.edu/reference/faq.html
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Date: 08 May 2007 04:04:58
From: Chris.B
Subject: Re: 4 inch reflector can't resolve Mars at all
|
I find tracking allows the eye to relax and settle on the object. The
eye can then focus naturally and begin to scan over the object for
fine detail.
If you want to see the effect of an altazimuth mounting just switch
off the equatorial's drive motor. Then try to see the same detail in
the few moments you have before it races out of the field of view.
Most people seem to use too high a power which only magnifies the
faults in the system. Particularly in an altazimuth where shake may
also be present as the telescope is moved. Resulting in an even
briefer chance to lock onto the speeding and bouncing fuzzy ball! :-)
Perhaps younger people have faster reactions and can spot planetary
detail in a fuzzy, bouncing object as it shoots across the field of
view? I know I can't.
The buttery movement of a Dob is indeed a rare tactile pleasure but
(surely) has nothing to do with planetary observation of fine detail?
"Obverse" and "obtuse" are better words to describe its use for such a
task.
Having said that, the use of a Dob where it allows greater aperture
within one's limited budget is far better than a much smaller
telescope on a wobbly but decorative equatorial for the same price.
Better still IMO is to use an oversized, secondhand equatorial
mounting from the past few decades. Let it carry a secondhand, long
focus 8" reflector or 6"refractor. You won't be able to move the
mounting, because of its weight, but who cares? Leave it outside on a
permanent pipe pier and just drop the telescope into the rings when
you want to use it. Unless you live in a high risk area a secure,
padlocked box over the mounting should protect it.
http://mysite.wanadoo-members.co.uk/fullerscopes_mk4/index.jhtml
|
| | |
Date: 08 May 2007 08:00:09
From: Dennis Woos
Subject: Re: 4 inch reflector can't resolve Mars at all
|
> Most people seem to use too high a power which only magnifies the
> faults in the system. Particularly in an altazimuth where shake may
> also be present as the telescope is moved. Resulting in an even
> briefer chance to lock onto the speeding and bouncing fuzzy ball! :-)
>
> Perhaps younger people have faster reactions and can spot planetary
> detail in a fuzzy, bouncing object as it shoots across the field of
> view? I know I can't.
>
> The buttery movement of a Dob is indeed a rare tactile pleasure but
> (surely) has nothing to do with planetary observation of fine detail?
> "Obverse" and "obtuse" are better words to describe its use for such a
> task.
I don't see that "bouncing" has anything to do with it. No one is
advocating continuously tracking at any power, let alone high power. The
target is allowed to drift through the field, providing an extremely smooth
"bounce" free view. The value of "buttery" smooth movement is in the ease
of positioning the target at the edge of the field in preparation for again
observing it as it passes through the field. So far as "fuzzy" goes, that
is an optical problem that has nothing to do with the kind of mount.
I certainly don't claim that a mount which tracks at high power is anything
but wonderful. However, my sons and I are perfectly happy observing at high
powers with our dobs. It has become so natural and intuitive that the
"tracking" is simply not noticed. Finally, I have often been pleasantly
surprised by how quickly folks who are unacustomed to using a dob pick up
the technique. Maybe it is not for everyone, but I believe that many folks
can and do adapt without problem.
Dennis
|
| | | |
Date: 09 May 2007 18:44:00
From: William Hamblen
Subject: Re: 4 inch reflector can't resolve Mars at all
|
On Tue, 8 May 2007 08:00:09 -0400, "Dennis Woos" <dpwoos@gmavt.net >
wrote:
>I certainly don't claim that a mount which tracks at high power is anything
>but wonderful. However, my sons and I are perfectly happy observing at high
>powers with our dobs. It has become so natural and intuitive that the
>"tracking" is simply not noticed. Finally, I have often been pleasantly
>surprised by how quickly folks who are unacustomed to using a dob pick up
>the technique. Maybe it is not for everyone, but I believe that many folks
>can and do adapt without problem.
My telescope is on an equatorial mount, but I seldom turn on the motor
when I'm not imaging or showing objects to someone else. I just turn
the polar axis slow motion as needed.
A driven mount is handy when you are at a star party and have people
lined up for a look through the eyepiece.
Bud
--
The night is just the shadow of the Earth.
|
| |
Date: 08 May 2007 03:06:37
From:
Subject: Re: 4 inch reflector can't resolve Mars at all
|
On May 8, 3:42 am, pau...@saaf.se (Paul Schlyter) wrote:
> In article <133u56pa8qqd...@corp.supernews.com>,
>
> Dennis Woos <dpw...@gmavt.net> wrote:
> > I too highly value excellent optics, and not just for the superior
> > views on good nights. It has seemed to me that scopes with top-notch
> > optics are more immune to bad seeing. I have always assumed that this
> > is due to excellent optics being limited only by the seeing and not
> > additionally by optical problems, and so on any given night not as
> > likely to exceed some threshhold of distortion which is objectionable.
> > In any case, I have experienced quite a few nights when many folks are
> > complaining about the seeing, and yet the scopes with the best optics
> > are still able to provide very enjoyable views at higher powers.
>
> That sounds weird! On an evening with bad seeing, the difference
> between a good scope and a bad scope ought to be less noticeable.
> It's only during a night with really good scope that a good telescope
> ought to shine and show its superiority over the less good scope.
>
> Or perhaps you are referring to "local seeing" within the scope
> itself? I.e. local airstreams inside and near the scope, caused by
> uneven cooling of the scope? In that respect, scopes can indeed be
> different.
>
The following is somewhat oversimplified, but imagine that a mediocre
telescope, used under perfect seeing, could equal the performance of a
perfect telescope used under mediocre seeing. Now use both scopes,
side by side, under seeing conditions somewhere between mediocre and
perfect. Which will work better?
|
| | |
Date: 09 May 2007 07:42:45
From: Paul Schlyter
Subject: Re: 4 inch reflector can't resolve Mars at all
|
In article <1178618797.815114.71650@q75g2000hsh.googlegroups.com >,
<wsnell01@hotmail.com > wrote:
> On May 8, 3:42 am, pau...@saaf.se (Paul Schlyter) wrote:
>> In article <133u56pa8qqd...@corp.supernews.com>,
>>
>> Dennis Woos <dpw...@gmavt.net> wrote:
>>> I too highly value excellent optics, and not just for the superior
>>> views on good nights. It has seemed to me that scopes with top-notch
>>> optics are more immune to bad seeing. I have always assumed that this
>>> is due to excellent optics being limited only by the seeing and not
>>> additionally by optical problems, and so on any given night not as
>>> likely to exceed some threshhold of distortion which is objectionable.
>>> In any case, I have experienced quite a few nights when many folks are
>>> complaining about the seeing, and yet the scopes with the best optics
>>> are still able to provide very enjoyable views at higher powers.
>>
>> That sounds weird! On an evening with bad seeing, the difference
>> between a good scope and a bad scope ought to be less noticeable.
>> It's only during a night with really good scope that a good telescope
>> ought to shine and show its superiority over the less good scope.
>>
>> Or perhaps you are referring to "local seeing" within the scope
>> itself? I.e. local airstreams inside and near the scope, caused by
>> uneven cooling of the scope? In that respect, scopes can indeed be
>> different.
>
> The following is somewhat oversimplified, but imagine that a mediocre
> telescope, used under perfect seeing, could equal the performance of a
> perfect telescope used under mediocre seeing. Now use both scopes,
> side by side, under seeing conditions somewhere between mediocre and
> perfect. Which will work better?
The perfect telescope should always work better than the mediocre
telescope, no matter the seeing conditions, of course - if we assume
both scope are subjected to the same seeing conditions. However, as
the seeing degrades, the difference between the perfect scope and the
mediocre scope ought to become less noticeable.
--
----------------------------------------------------------------
Paul Schlyter, Grev Turegatan 40, SE-114 38 Stockholm, SWEDEN
e-mail: pausch at stockholm dot bostream dot se
WWW: http://stjarnhimlen.se/
|
| | |
Date: 08 May 2007 06:22:11
From: Dennis Woos
Subject: Re: 4 inch reflector can't resolve Mars at all
|
> The following is somewhat oversimplified, but imagine that a mediocre
> telescope, used under perfect seeing, could equal the performance of a
> perfect telescope used under mediocre seeing. Now use both scopes,
> side by side, under seeing conditions somewhere between mediocre and
> perfect. Which will work better?
>
Yes, this example illustrates my contention. If we think of "seeing" as
another aberation in the optical train, then it is seems to me that it is
additive. 1/4 wave seeing plus 1/4 wave optics equals 1/2 wave overall,
whereas for top notch optics 1/4 wave seeing plus 1/10 wave optics equals
approximately 1/3 wave overall.
Dennis
|
| | | |
Date: 09 May 2007 07:42:45
From: Paul Schlyter
Subject: Re: 4 inch reflector can't resolve Mars at all
|
In article <1340jqnfvtqsm03@corp.supernews.com >,
Dennis Woos <dpwoos@gmavt.net > wrote:
>> The following is somewhat oversimplified, but imagine that a mediocre
>> telescope, used under perfect seeing, could equal the performance of a
>> perfect telescope used under mediocre seeing. Now use both scopes,
>> side by side, under seeing conditions somewhere between mediocre and
>> perfect. Which will work better?
>
> Yes, this example illustrates my contention. If we think of "seeing" as
> another aberation in the optical train, then it is seems to me that it is
> additive. 1/4 wave seeing plus 1/4 wave optics equals 1/2 wave overall,
> whereas for top notch optics 1/4 wave seeing plus 1/10 wave optics equals
> approximately 1/3 wave overall.
>
> Dennis
More than waves matter - aperture matters too. A small telescope ought
to be less sensitive to non-perfect seeing conditions than a large scope,
because the smaller scope does not resolve as well as the larger scope,
even if both scopes are, say, 1/8 wave.
--
----------------------------------------------------------------
Paul Schlyter, Grev Turegatan 40, SE-114 38 Stockholm, SWEDEN
e-mail: pausch at stockholm dot bostream dot se
WWW: http://stjarnhimlen.se/
|
| | | |
Date: 08 May 2007 07:31:58
From: Brian Tung
Subject: Re: 4 inch reflector can't resolve Mars at all
|
Dennis Woos wrote:
> Yes, this example illustrates my contention. If we think of "seeing" as
> another aberation in the optical train, then it is seems to me that it is
> additive. 1/4 wave seeing plus 1/4 wave optics equals 1/2 wave overall,
> whereas for top notch optics 1/4 wave seeing plus 1/10 wave optics equals
> approximately 1/3 wave overall.
Uncorrelated wavefront deviations (such as seeing and optical surface
errors) do not add linearly; they add RMS. So 1/4-wave plus 1/4-wave
equals a little worse than 1/3-wave, whereas 1/4-wave plus 1/10-wave is
about 1/4-wave.
Seeing does tend to minimize the differences between good and bad; it
of course does not eliminate it.
--
Brian Tung <brian@isi.edu >
The Astronomy Corner at http://astro.isi.edu/
Unofficial C5+ Home Page at http://astro.isi.edu/c5plus/
The PleiadAtlas Home Page at http://astro.isi.edu/pleiadatlas/
My Own Personal FAQ (SAA) at http://astro.isi.edu/reference/faq.html
|
| | | | |
Date: 08 May 2007 15:06:56
From: Dennis Woos
Subject: Re: 4 inch reflector can't resolve Mars at all
|
>> Yes, this example illustrates my contention. If we think of "seeing" as
>> another aberation in the optical train, then it is seems to me that it is
>> additive. 1/4 wave seeing plus 1/4 wave optics equals 1/2 wave overall,
>> whereas for top notch optics 1/4 wave seeing plus 1/10 wave optics equals
>> approximately 1/3 wave overall.
>
> Uncorrelated wavefront deviations (such as seeing and optical surface
> errors) do not add linearly; they add RMS. So 1/4-wave plus 1/4-wave
> equals a little worse than 1/3-wave, whereas 1/4-wave plus 1/10-wave is
> about 1/4-wave.
>
> Seeing does tend to minimize the differences between good and bad; it
> of course does not eliminate it.
>
> --
> Brian Tung <brian@isi.edu>
Thanks for the clarification on the physics/optics. You know, it seems to
me that there are almost certainly physiological factors at work as well.
These vary from one individual to another, and who knows how these add up?
Sometimes I wonder if all of the optical tests and ratings are not as
significant as we think, given the wide variations in people's eyesight. An
example of this is the whole exit pupil thing, where folks cite 7mm as if it
was some kind of standard. An opthalmologist who spoke at one of our club
meetings related that he has many older patients whom he believes never
exceed a 3-4mm dilation when dark adapted.
Dennis
|
| | | | | |
Date: 09 May 2007 07:42:45
From: Paul Schlyter
Subject: Re: 4 inch reflector can't resolve Mars at all
|
In article <1341ij5p02h7922@corp.supernews.com >,
Dennis Woos <dpwoos@gmavt.net > wrote:
>>> Yes, this example illustrates my contention. If we think of "seeing" as
>>> another aberation in the optical train, then it is seems to me that it is
>>> additive. 1/4 wave seeing plus 1/4 wave optics equals 1/2 wave overall,
>>> whereas for top notch optics 1/4 wave seeing plus 1/10 wave optics equals
>>> approximately 1/3 wave overall.
>>
>> Uncorrelated wavefront deviations (such as seeing and optical surface
>> errors) do not add linearly; they add RMS. So 1/4-wave plus 1/4-wave
>> equals a little worse than 1/3-wave, whereas 1/4-wave plus 1/10-wave is
>> about 1/4-wave.
>>
>> Seeing does tend to minimize the differences between good and bad; it
>> of course does not eliminate it.
>>
>> --
>> Brian Tung <brian@isi.edu>
>
> Thanks for the clarification on the physics/optics. You know, it seems to
> me that there are almost certainly physiological factors at work as well.
> These vary from one individual to another, and who knows how these add up?
> Sometimes I wonder if all of the optical tests and ratings are not as
> significant as we think, given the wide variations in people's eyesight. An
> example of this is the whole exit pupil thing, where folks cite 7mm as if it
> was some kind of standard. An opthalmologist who spoke at one of our club
> meetings related that he has many older patients whom he believes never
> exceed a 3-4mm dilation when dark adapted.
>
> Dennis
My own maximum pupil dilatation is around 5 mm. Which means it would
be a waste for me to use 7x50 binoculars - I should use e.g. 7x35 or
10x50 binos instead.
Generally, as one grows older, the maximum pupil size will shrink.
--
----------------------------------------------------------------
Paul Schlyter, Grev Turegatan 40, SE-114 38 Stockholm, SWEDEN
e-mail: pausch at stockholm dot bostream dot se
WWW: http://stjarnhimlen.se/
|
| | | | | | |
Date: 09 May 2007 07:57:41
From: Brian Tung
Subject: Re: 4 inch reflector can't resolve Mars at all
|
Paul Schlyter wrote:
> My own maximum pupil dilatation is around 5 mm. Which means it would
> be a waste for me to use 7x50 binoculars - I should use e.g. 7x35 or
> 10x50 binos instead.
To a certain extent, yes--but having a bigger exit pupil than your eye's
pupil does yield the benefit of making it easier to position your eye,
doesn't it?
--
Brian Tung <brian@isi.edu >
The Astronomy Corner at http://astro.isi.edu/
Unofficial C5+ Home Page at http://astro.isi.edu/c5plus/
The PleiadAtlas Home Page at http://astro.isi.edu/pleiadatlas/
My Own Personal FAQ (SAA) at http://astro.isi.edu/reference/faq.html
|
| |
Date: 07 May 2007 06:16:08
From:
Subject: Re: 4 inch reflector can't resolve Mars at all
|
On May 7, 2:37 am, David Knisely <KA0...@navix.net > wrote:
> wsnell01 wrote:
> > You are making coma and astigmatism sound like some kind of show-
> > stopping disasters that would tend to disqualify an f/6 Newtonian from
> > consideration, unless they are fixed.
>
> No, *you* are putting words in my mouth. I said no such thing, nor did
> I even imply it. I was responding to Chris Peterson's response,
> " That's a sign of uncritical observing, plain and simple. In an
> uncorrected Newt, coma is significant."
>
> I pointed out that the outer field astigmatism in many eyepieces when
> used at f/6 often swamps the coma (and is often mistakenly reported as
> coma by some less-experienced amateurs). The coma is basically a
> *minor* issue and not a "show stopping disaster". The astigmatism isn't
> a show-stopper either, but it is an issue which was relevant when
> talking about the amount of coma in an 8 inch f/6 (which was what I was
> addressing). Some people are bothered by it and some aren't depending
> on what they are looking at.
What you were actually doing earlier was dismissing coma as a problem
(so far, so good) by replacing it with astigmatism as a problem, when
in fact neither is a problem big enough to worry about, especially
when you consider all of the other factors.
>
> > When
> > you consider what a superb value a typical 8-inch Dob really is, coma,
> > astigmatism, etc., become -completely- irrelevant.
>
> Again, I was never trying to badmouth an inch Dob. I have an 8 inch f/7
> Newtonian which works just fine, as well as a 10 inch f/5.6, (both home
> built), so I have no problems recommending a Newtonian.
>
> > Or let me put it this way:
>
> > I have $500 to spend on a telescope and accessories for looking at
> > Mars' in the next few months. What should I buy?
>
> I would probably save my money and purchase the finest set of 10 inch
> f/6 optics I could find for constructing a planetary instrument.
> However, if someone just wants a scope *now*, a 10 inch commerical Dob
> would not be much more than $600. For higher powers, I might go with a
> 5-8mm Speers Waler eyepiece, although a decent Barlow and a 10mm Plossl
> would probably work about as well. Also, a light red filter is useful
> for increasing the contrast of the dark markings (Wratten #23a would be
> good). Clear skies to you.
>
I have a $500 budget, of which a Speers-Waler eyepiece would use up at
least half. So I guess I'll have to stick with the XT-8, along with
maybe a 3x Barlow.
|
| | |
Date: 08 May 2007 23:20:23
From: David Knisely
Subject: Re: 4 inch reflector can't resolve Mars at all
|
wsnell01 wrote:
> What you were actually doing earlier was dismissing coma as a problem
> (so far, so good) by replacing it with astigmatism as a problem, when
> in fact neither is a problem big enough to worry about, especially
> when you consider all of the other factors.
No, again, you are missing the point. Any f/6 scope will make some of
the less corrected eyepiece designs generate visible astigmatism near
the outer edge of the field. It is a problem which in many cases is
larger than that of the coma produced by an 8 inch f/6 paraboloid. The
coma is small, small enough that the off-axis astigmatism shown with
many eyepieces is enough to obscure it to a large extent. The
astigmatism isn't "replacing" anything. It is an eyepiece-related
problem with f/6 light cones and many of the more common bargain
eyepiece designs, period. There were not any other factors mentioned,
nor were they needed, as that was *not* the point of discussion.
--
David W. Knisely KA0CZC@navix.net
Prairie Astronomy Club: http://www.prairieastronomyclub.org
Hyde Memorial Observatory: http://www.hydeobservatory.info/
**********************************************
* Attend the 14th Annual NEBRASKA STAR PARTY *
* July 15th-20th, 2007, Merritt Reservoir *
* http://www.NebraskaStarParty.org *
**********************************************
|
| | | |
Date: 09 May 2007 18:47:55
From: William Hamblen
Subject: Re: 4 inch reflector can't resolve Mars at all
|
On Tue, 08 May 2007 23:20:23 -0500, David Knisely <KA0CZC@navix.net >
wrote:
>No, again, you are missing the point. Any f/6 scope will make some of
>the less corrected eyepiece designs generate visible astigmatism near
>the outer edge of the field. It is a problem which in many cases is
>larger than that of the coma produced by an 8 inch f/6 paraboloid. The
>coma is small, small enough that the off-axis astigmatism shown with
>many eyepieces is enough to obscure it to a large extent. The
>astigmatism isn't "replacing" anything. It is an eyepiece-related
>problem with f/6 light cones and many of the more common bargain
>eyepiece designs, period. There were not any other factors mentioned,
>nor were they needed, as that was *not* the point of discussion.
The mirror has off-axis astigmatism, too. The amount of astigmatism
in a parabolic mirror is close to the amount of coma. I don't think
either is particularly important when you are not making pictures,
because you naturally put what you want to see near the center of the
field of view.
Bud
--
The night is just the shadow of the Earth.
|
| | | |
Date: 09 May 2007 09:26:25
From: Dennis Woos
Subject: Re: 4 inch reflector can't resolve Mars at all
|
>> What you were actually doing earlier was dismissing coma as a problem
>> (so far, so good) by replacing it with astigmatism as a problem, when
>> in fact neither is a problem big enough to worry about, especially
>> when you consider all of the other factors.
>
> No, again, you are missing the point. Any f/6 scope will make some of the
> less corrected eyepiece designs generate visible astigmatism near the
> outer edge of the field. It is a problem which in many cases is larger
> than that of the coma produced by an 8 inch f/6 paraboloid. The coma is
> small, small enough that the off-axis astigmatism shown with many
> eyepieces is enough to obscure it to a large extent. The astigmatism
> isn't "replacing" anything. It is an eyepiece-related problem with f/6
> light cones and many of the more common bargain eyepiece designs, period.
> There were not any other factors mentioned, nor were they needed, as that
> was *not* the point of discussion.
>
Another factor is astigmatism introduced by the eye. I know that at low
power I see some astig that folks with better eyesight (like my older son)
say is not there. This astig is severe enough to easily mask any coma. My
glasses do not correct for astigmatism, and I don't usually wear them for
observing anyway. At higher powers this astig is gone. I am certainly
going to try and detect coma in our 10" f/6 scope the next chance I get, and
will get my son to do so as well. However, I think it is fair to say that
it is not a big issue.
Dennis
|
| | | | |
Date: 09 May 2007 10:20:27
From: David G. Nagel
Subject: Re: 4 inch reflector can't resolve Mars at all
|
Dennis Woos wrote:
>>> What you were actually doing earlier was dismissing coma as a problem
>>> (so far, so good) by replacing it with astigmatism as a problem, when
>>> in fact neither is a problem big enough to worry about, especially
>>> when you consider all of the other factors.
>> No, again, you are missing the point. Any f/6 scope will make some of the
>> less corrected eyepiece designs generate visible astigmatism near the
>> outer edge of the field. It is a problem which in many cases is larger
>> than that of the coma produced by an 8 inch f/6 paraboloid. The coma is
>> small, small enough that the off-axis astigmatism shown with many
>> eyepieces is enough to obscure it to a large extent. The astigmatism
>> isn't "replacing" anything. It is an eyepiece-related problem with f/6
>> light cones and many of the more common bargain eyepiece designs, period.
>> There were not any other factors mentioned, nor were they needed, as that
>> was *not* the point of discussion.
>>
>
> Another factor is astigmatism introduced by the eye. I know that at low
> power I see some astig that folks with better eyesight (like my older son)
> say is not there. This astig is severe enough to easily mask any coma. My
> glasses do not correct for astigmatism, and I don't usually wear them for
> observing anyway. At higher powers this astig is gone. I am certainly
> going to try and detect coma in our 10" f/6 scope the next chance I get, and
> will get my son to do so as well. However, I think it is fair to say that
> it is not a big issue.
>
> Dennis
>
>
Dennis;
I have to assume that if your glasses don't correct for astigmatism that
either your eye doctor is incompentant or there is some other medical
reason for you not having corrected lens in your glasses. It is one of
the standard tests made during an examination to determine the
correction for astigmatism. You need to check with another eye doctor
about this.
Dave
blind as a bat without my specs.
|
| | | | | |
Date: 09 May 2007 11:54:43
From: Dennis Woos
Subject: Re: 4 inch reflector can't resolve Mars at all
|
> I have to assume that if your glasses don't correct for astigmatism that
> either your eye doctor is incompentant or there is some other medical
> reason for you not having corrected lens in your glasses. It is one of the
> standard tests made during an examination to determine the correction for
> astigmatism. You need to check with another eye doctor about this.
>
> Dave
> blind as a bat without my specs.
I just got off the phone with my eye doctor's office, and I do have some
astig correction, but only for my right eye. I observe with my left eye.
They also told me that my prescription is from Dec. 2005, so I assume I now
have developed some astig in my left eye as well. In any case, it is not
something I notice at any time other than low-power observing, so I believe
that the amount of astig (though easily detected in the eyepiece) is small
by daytime standards. I will definitely talk to my doc about this at my
next visit. Thanks.
Dennis
|
| | | | | |
Date: 09 May 2007 15:44:47
From: Chris L Peterson
Subject: Re: 4 inch reflector can't resolve Mars at all
|
On Wed, 09 May 2007 10:20:27 -0500, "David G. Nagel" <nagel@core.com >
wrote:
>I have to assume that if your glasses don't correct for astigmatism that
>either your eye doctor is incompentant or there is some other medical
>reason for you not having corrected lens in your glasses. It is one of
>the standard tests made during an examination to determine the
>correction for astigmatism. You need to check with another eye doctor
>about this.
Astigmatism is only partly correctable. That's because the correction
applied is classical: a purely cylindrical correction applied to a
spherical lens along one axis. What is called "astigmatism" in the eye,
however, is far from classical, and results from the fact that the
cornea has a complex shape that is aspherical, and with "astigmatism"
that isn't cylindrical. At best, corrective lenses provide an
approximate correction optimized for a pupil diameter typically less
than maximum. So even with a very well designed pair of glasses or
contacts, it is quite common to see astigmatism and other aberrations
when observing (especially at low power, where more of the cornea is
involved).
You can achieve near perfect correction only with hard contact lenses,
but hardly anybody uses those anymore.
_________________________________________________
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com
|
| |
Date: 07 May 2007 05:28:18
From:
Subject: Re: 4 inch reflector can't resolve Mars at all
|
On May 7, 3:41 am, pau...@saaf.se (Paul Schlyter) wrote:
> In article <1178453930.918291.294...@w5g2000hsg.googlegroups.com>,
>
>
>
> <wsnel...@hotmail.com> wrote:
> > On May 6, 6:42 am, pau...@saaf.se (Paul Schlyter) wrote:
> .............
> >> Very true.... with that 2.4" refractor I got as a kid, I was unable
> >> to see any details on Mars during the 1963 and 1965 oppositions. Not
> >> until the 1967 opposition I was able to see Syrtis Major, Sinus
> >> Meridiani and a few other of the largest albedo features on Mars,
> >> with that instrument.
>
> > Think about what you might have been able to see if you had owned an 8-
> > inch Newtonian on an alt-az mount in '67 (or even '63 or '65)
>
> You don't necessarily have to own an instrument to look through it.... ;-)
True, but don't count on getting very much time on someone else's
telescope during a good Mars apparition; the owner might want to use
it too. :-)
>
> Actually, I hade the good fortune to be able to look through an 8-inch
> refractor (yes, refractor, not reflector) on an equatorial clock driven
> mount in the fall of '63. Yes, it was a difference! But the look
> through a 20-inch refractor (yes, refractor - no typo here) was even
> more impressive....
>
> Btw I don't know about any 8-inch Newtonians on alt-az mounts from
> that time. Back then, if you went for a telescope as big as that, it
> was taken for granted that it should of course also have an equatorial
> mounting - anything elss than that was considered a waste on such an
> instrument! This was well before the age of the Dob.
>
Texereau's book (written in the 50's?) had plans for an alt-az mounted
8-inch Newtonian. If I had been able to scrape together enough to buy
an eight- or ten-inch mirror in my early days, before the Dob
revolution, this is what I would have built. It would have been a
crude, ugly but very effective telescope.
|
| |
Date: 06 May 2007 07:41:23
From:
Subject: Re: 4 inch reflector can't resolve Mars at all
|
On May 6, 9:19 am, "Joe S." <non...@nosuch.net > wrote:
> "Bullseye" <b...@ei.com> wrote in message
>
> news:mcvh33592uhm1eo7c4uh1ib2ejnqkhfvib@4ax.com...
>
> >I have a Nexstar 114GT and it can give visuals of the moon nicely
> > (most scopes can I think) but I can't see sqwat when I point to Mars.
> > I pointed to it 1-2 years ago when it was all over the news that it
> > was close to Earth, but all I could see was a pink little ball, no
> > features at all. Also in Saturn all I could see is a tiny little dot
> > with a tiny circle around it. I've centered the scope and adjusted it
> > all the ways I'm supposed to to get the best image (I've forgotten the
> > exact terms that are used since I've ditched astronomy for awhile),
> > but trust me I did. I just want to sell this sucker and get a new one.
> > Can anyone recommend the best 4 inch reflectors out there for less
> > than $500? Or maybe a very good 8 inch dob for less than $500?
>
> How much longer can this thread continue??
Begin sarcasm:
Probably as soon as someone figures out how to solve, inexpensively,
the horrible, debilitating problems that plague the common Dobsonian,
namely coma, astigmatism, central obstruction, lack of tracking, etc.,
any one of which seems to be enough to make them utterly worthless.
End sarcasm.
|
| |
Date: 06 May 2007 07:34:17
From:
Subject: Re: 4 inch reflector can't resolve Mars at all
|
On May 6, 9:15 am, David Knisely <KA0...@navix.net > wrote:
> wsnell01 wrote:
> > Neither coma nor astigmatism is a "problem" in an 8-inch f/6 Dob
> > since, as a practical matter, there is no other telescope that can
> > potentially provide the same light gathering, resolution and contrast
> > or as stable a mount for such a low price.
>
> Well, I'm afraid that the above statement is somewhat irrelevant, as the
> practicality of an 8 inch f/6 Dobsonian was not what I was talking
> about. At f/6, less complex moderate to wide-field eyepiece designs
> tend to generate a visible amount off-axis astigmatism in star images
> located close to the field stop. This can be remedied by either using a
> more complex and better corrected eyepiece (Naglers, Panoptics, etc.) or
> by using a Barlow in the system to extend the focal length and make it
> easier for the eyepiece to handle. However, as I indicated, the coma at
> f/6 is rather small and tends to get covered up by the off-axis
> astigmatism present in many of the budget eyepieces.
You are making coma and astigmatism sound like some kind of show-
stopping disasters that would tend to disqualify an f/6 Newtonian from
consideration, unless they are fixed. For someone on a budget,
Plossls work well enough even at fast to moderate f-ratios and for
planetary observing you will probably be using a Barlow anyway. When
you consider what a superb value a typical 8-inch Dob really is, coma,
astigmatism, etc., become -completely- irrelevant.
Or let me put it this way:
I have $500 to spend on a telescope and accessories for looking at
Mars' in the next few months. What should I buy?
|
| | |
Date: 07 May 2007 01:37:36
From: David Knisely
Subject: Re: 4 inch reflector can't resolve Mars at all
|
wsnell01 wrote:
> You are making coma and astigmatism sound like some kind of show-
> stopping disasters that would tend to disqualify an f/6 Newtonian from
> consideration, unless they are fixed.
No, *you* are putting words in my mouth. I said no such thing, nor did
I even imply it. I was responding to Chris Peterson's response,
" That's a sign of uncritical observing, plain and simple. In an
uncorrected Newt, coma is significant."
I pointed out that the outer field astigmatism in many eyepieces when
used at f/6 often swamps the coma (and is often mistakenly reported as
coma by some less-experienced amateurs). The coma is basically a
*minor* issue and not a "show stopping disaster". The astigmatism isn't
a show-stopper either, but it is an issue which was relevant when
talking about the amount of coma in an 8 inch f/6 (which was what I was
addressing). Some people are bothered by it and some aren't depending
on what they are looking at.
> When
> you consider what a superb value a typical 8-inch Dob really is, coma,
> astigmatism, etc., become -completely- irrelevant.
Again, I was never trying to badmouth an inch Dob. I have an 8 inch f/7
Newtonian which works just fine, as well as a 10 inch f/5.6, (both home
built), so I have no problems recommending a Newtonian.
> Or let me put it this way:
>
> I have $500 to spend on a telescope and accessories for looking at
> Mars' in the next few months. What should I buy?
I would probably save my money and purchase the finest set of 10 inch
f/6 optics I could find for constructing a planetary instrument.
However, if someone just wants a scope *now*, a 10 inch commerical Dob
would not be much more than $600. For higher powers, I might go with a
5-8mm Speers Waler eyepiece, although a decent Barlow and a 10mm Plossl
would probably work about as well. Also, a light red filter is useful
for increasing the contrast of the dark markings (Wratten #23a would be
good). Clear skies to you.
--
David W. Knisely KA0CZC@navix.net
Prairie Astronomy Club: http://www.prairieastronomyclub.org
Hyde Memorial Observatory: http://www.hydeobservatory.info/
**********************************************
* Attend the 14th Annual NEBRASKA STAR PARTY *
* July 15th-20th, 2007, Merritt Reservoir *
* http://www.NebraskaStarParty.org *
**********************************************
|
| | | |
Date: 07 May 2007 08:00:22
From: Dennis Woos
Subject: Re: 4 inch reflector can't resolve Mars at all
|
> I would probably save my money and purchase the finest set of 10 inch f/6
> optics I could find for constructing a planetary instrument. However, if
> someone just wants a scope *now*, a 10 inch commerical Dob would not be
> much more than $600. For higher powers, I might go with a 5-8mm Speers
> Waler eyepiece, although a decent Barlow and a 10mm Plossl would probably
> work about as well. Also, a light red filter is useful for increasing the
> contrast of the dark markings (Wratten #23a would be good). Clear skies
> to you.
>
I too highly value excellent optics, and not just for the superior views on
good nights. It has seemed to me that scopes with top-notch optics are more
immune to bad seeing. I have always assumed that this is due to excellent
optics being limited only by the seeing and not additionally by optical
problems, and so on any given night not as likely to exceed some threshhold
of distortion which is objectionable. In any case, I have experienced quite
a few nights when many folks are complaining about the seeing, and yet the
scopes with the best optics are still able to provide very enjoyable views
at higher powers.
The 5-8mm Speers Waler is at the top of my list of eyepieces that I would
love to try! Finally, the Wratten #85 salmon is a favorite of many of our
club's members with smaller aperture scopes for Mars. Maybe it performs
similarly to a red filter, but passes more light and so provides a bit
brighter image?
Dennis
|
| | | | |
Date: 08 May 2007 07:42:10
From: Paul Schlyter
Subject: Re: 4 inch reflector can't resolve Mars at all
|
In article <133u56pa8qqdjea@corp.supernews.com >,
Dennis Woos <dpwoos@gmavt.net > wrote:
> I too highly value excellent optics, and not just for the superior
> views on good nights. It has seemed to me that scopes with top-notch
> optics are more immune to bad seeing. I have always assumed that this
> is due to excellent optics being limited only by the seeing and not
> additionally by optical problems, and so on any given night not as
> likely to exceed some threshhold of distortion which is objectionable.
> In any case, I have experienced quite a few nights when many folks are
> complaining about the seeing, and yet the scopes with the best optics
> are still able to provide very enjoyable views at higher powers.
That sounds weird! On an evening with bad seeing, the difference
between a good scope and a bad scope ought to be less noticeable.
It's only during a night with really good scope that a good telescope
ought to shine and show its superiority over the less good scope.
Or perhaps you are referring to "local seeing" within the scope
itself? I.e. local airstreams inside and near the scope, caused by
uneven cooling of the scope? In that respect, scopes can indeed be
different.
--
----------------------------------------------------------------
Paul Schlyter, Grev Turegatan 40, SE-114 38 Stockholm, SWEDEN
e-mail: pausch at stockholm dot bostream dot se
WWW: http://stjarnhimlen.se/
|
| |
Date: 06 May 2007 09:19:24
From: Joe S.
Subject: Re: 4 inch reflector can't resolve Mars at all
|
"Bullseye" <bulls@ei.com > wrote in message
news:mcvh33592uhm1eo7c4uh1ib2ejnqkhfvib@4ax.com...
>I have a Nexstar 114GT and it can give visuals of the moon nicely
> (most scopes can I think) but I can't see sqwat when I point to Mars.
> I pointed to it 1-2 years ago when it was all over the news that it
> was close to Earth, but all I could see was a pink little ball, no
> features at all. Also in Saturn all I could see is a tiny little dot
> with a tiny circle around it. I've centered the scope and adjusted it
> all the ways I'm supposed to to get the best image (I've forgotten the
> exact terms that are used since I've ditched astronomy for awhile),
> but trust me I did. I just want to sell this sucker and get a new one.
> Can anyone recommend the best 4 inch reflectors out there for less
> than $500? Or maybe a very good 8 inch dob for less than $500?
How much longer can this thread continue??
|
| | |
Date: 06 May 2007 14:45:54
From: Guy Macon
Subject: Re: 4 inch reflector can't resolve Mars at all
|
Joe S. wrote:
>How much longer can this thread continue??
THE STANDARD ADVICE:
There is a way to influence what gets discussed in a newsgroup that
works well, and another way that has never worked no matter how many
people have tried it.
What works: Post articles on the topic you wish to see discussed
and participate in the resulting discussion. Use killfiles and
filters so that you don't see the articles that you dislike.
If you don't know how to use a killfile, use good old fashioned
discipline and don't read posts by people who post articles that
you dislike. Never, ever respond to articles that you dislike.
What doesn't work: Respond to articles that you dislike, complain
about articles that you dislike, complain about posters that you
dislike, complain about how terrible everyone else is for not posting
what you want them to post. Talk about how to respond to articles
that you dislike. Make the articles that you dislike the center of
attention, the main topic of discussion, and a personal crusade.
-Guy Macon
|
| |
Date: 06 May 2007 05:18:50
From:
Subject: Re: 4 inch reflector can't resolve Mars at all
|
On May 6, 6:42 am, pau...@saaf.se (Paul Schlyter) wrote:
> In article <1178366419.072601.215...@p77g2000hsh.googlegroups.com>,
>
>
>
> <wsnel...@hotmail.com> wrote:
> > On May 5, 4:19 am, David Knisely <KA0...@navix.net> wrote:
> >> Chris L. Peterson wrote:
> >>>> Finally, off axis coma is not a significant issue with an 8" f/6 newt, even
> >>>> >with wide-field eyepieces. In our 10" f/6 dob, we regularly experience
> >>>> >great high-power views while allowing the target to drift completely across
> >>>> >the field. I have never heard anyone else comment on coma when observing
> >>>> >with a newtonian of focal ratio in the range of 6 or higher.
>
> >>> That's a sign of uncritical observing, plain and simple. In an
> >>> uncorrected Newt, coma is significant. Its effect on the MTF is much
> >>> more important than central obstruction, for instance. Anybody who is a
> >>> good enough observer to see the difference in contrast between an
> >>> obstructed and unobstructed system will find the effects of coma much
> >>> more obvious.
>
> >> Unfortunately, coma is not usually the main problem in an 8 inch f/6.
> >> The most common problem is usually outer field astigmatism which, in
> >> most of the less-complex eyepiece designs, completely masks any coma
> >> that is present. Many people report the astigmatic appearance of outer
> >> field stars as "coma" when it really isn't. I had to use a
> >> well-corrected wide field eyepiece (Meade "original" 14mm Ultrawide)
> >> before I got to see "pure" coma in an f/6 scope. The Paracorr
> >> noticeably reduced the coma present, but in an f/6, I would still have
> >> to call the amount relatively small (especially when compared to the
> >> coma seen in something like an f/4.5 scope). Clear skies to you.
> > > --
>
> > Neither coma nor astigmatism is a "problem" in an 8-inch f/6 Dob
> > since, as a practical matter, there is no other telescope that can
> > potentially provide the same light gathering, resolution and contrast
> > or as stable a mount for such a low price.
>
> In other words, you get what you pay for.... ;-)
In the case of an 8-inch Dob, you get quite a bit more - compared to a
similarly priced 4-inch Go-To scope - when it comes down to what it
can show.
>
> But surely one should be able to see details on Mars with a 4" scope!
> I've seen details on Mars with a 2.4" f/15 refractor I got as a kid.
>
> > The main "problems" to
> > solve WRT to scope itself are collimation (not difficult), smooth
> > motion (easy to remedy), having an appropriate selection of eyepieces/
> > Barlows, and of course allowing enough time for the scope to "cool
> > down" after being brought outdoors.
>
> > Beyond that, the beginning observer will need to train his eye to see
> > detail and will need to be patient and persistent enough to be looking
> > through the eyepiece when the unsteady atmosphere settles down from
> > time to time.
>
> Very true.... with that 2.4" refractor I got as a kid, I was unable
> to see any details on Mars during the 1963 and 1965 oppositions. Not
> until the 1967 opposition I was able to see Syrtis Major, Sinus
> Meridiani and a few other of the largest albedo features on Mars,
> with that instrument.
>
Think about what you might have been able to see if you had owned an 8-
inch Newtonian on an alt-az mount in '67 (or even '63 or '65)
|
| | |
Date: 07 May 2007 07:41:57
From: Paul Schlyter
Subject: Re: 4 inch reflector can't resolve Mars at all
|
In article <1178453930.918291.294260@w5g2000hsg.googlegroups.com >,
<wsnell01@hotmail.com > wrote:
> On May 6, 6:42 am, pau...@saaf.se (Paul Schlyter) wrote:
.............
>> Very true.... with that 2.4" refractor I got as a kid, I was unable
>> to see any details on Mars during the 1963 and 1965 oppositions. Not
>> until the 1967 opposition I was able to see Syrtis Major, Sinus
>> Meridiani and a few other of the largest albedo features on Mars,
>> with that instrument.
>
> Think about what you might have been able to see if you had owned an 8-
> inch Newtonian on an alt-az mount in '67 (or even '63 or '65)
You don't necessarily have to own an instrument to look through it.... ;-)
Actually, I hade the good fortune to be able to look through an 8-inch
refractor (yes, refractor, not reflector) on an equatorial clock driven
mount in the fall of '63. Yes, it was a difference! But the look
through a 20-inch refractor (yes, refractor - no typo here) was even
more impressive....
Btw I don't know about any 8-inch Newtonians on alt-az mounts from
that time. Back then, if you went for a telescope as big as that, it
was taken for granted that it should of course also have an equatorial
mounting - anything elss than that was considered a waste on such an
instrument! This was well before the age of the Dob.
--
----------------------------------------------------------------
Paul Schlyter, Grev Turegatan 40, SE-114 38 Stockholm, SWEDEN
e-mail: pausch at stockholm dot bostream dot se
WWW: http://stjarnhimlen.se/
|
| |
Date: 05 May 2007 05:00:19
From:
Subject: Re: 4 inch reflector can't resolve Mars at all
|
On May 5, 4:19 am, David Knisely <KA0...@navix.net > wrote:
> Chris L. Peterson wrote:
> >> Finally, off axis coma is not a significant issue with an 8" f/6 newt, even
> >> >with wide-field eyepieces. In our 10" f/6 dob, we regularly experience
> >> >great high-power views while allowing the target to drift completely across
> >> >the field. I have never heard anyone else comment on coma when observing
> >> >with a newtonian of focal ratio in the range of 6 or higher.
>
> > That's a sign of uncritical observing, plain and simple. In an
> > uncorrected Newt, coma is significant. Its effect on the MTF is much
> > more important than central obstruction, for instance. Anybody who is a
> > good enough observer to see the difference in contrast between an
> > obstructed and unobstructed system will find the effects of coma much
> > more obvious.
>
> Unfortunately, coma is not usually the main problem in an 8 inch f/6.
> The most common problem is usually outer field astigmatism which, in
> most of the less-complex eyepiece designs, completely masks any coma
> that is present. Many people report the astigmatic appearance of outer
> field stars as "coma" when it really isn't. I had to use a
> well-corrected wide field eyepiece (Meade "original" 14mm Ultrawide)
> before I got to see "pure" coma in an f/6 scope. The Paracorr
> noticeably reduced the coma present, but in an f/6, I would still have
> to call the amount relatively small (especially when compared to the
> coma seen in something like an f/4.5 scope). Clear skies to you.
> --
Neither coma nor astigmatism is a "problem" in an 8-inch f/6 Dob
since, as a practical matter, there is no other telescope that can
potentially provide the same light gathering, resolution and contrast
or as stable a mount for such a low price. The main "problems" to
solve WRT to scope itself are collimation (not difficult), smooth
motion (easy to remedy), having an appropriate selection of eyepieces/
Barlows, and of course allowing enough time for the scope to "cool
down" after being brought outdoors.
Beyond that, the beginning observer will need to train his eye to see
detail and will need to be patient and persistent enough to be looking
through the eyepiece when the unsteady atmosphere settles down from
time to time.
|
| | |
Date: 06 May 2007 08:15:03
From: David Knisely
Subject: Re: 4 inch reflector can't resolve Mars at all
|
wsnell01 wrote:
> Neither coma nor astigmatism is a "problem" in an 8-inch f/6 Dob
> since, as a practical matter, there is no other telescope that can
> potentially provide the same light gathering, resolution and contrast
> or as stable a mount for such a low price.
Well, I'm afraid that the above statement is somewhat irrelevant, as the
practicality of an 8 inch f/6 Dobsonian was not what I was talking
about. At f/6, less complex moderate to wide-field eyepiece designs
tend to generate a visible amount off-axis astigmatism in star images
located close to the field stop. This can be remedied by either using a
more complex and better corrected eyepiece (Naglers, Panoptics, etc.) or
by using a Barlow in the system to extend the focal length and make it
easier for the eyepiece to handle. However, as I indicated, the coma at
f/6 is rather small and tends to get covered up by the off-axis
astigmatism present in many of the budget eyepieces. Clear skies to
you.
--
David W. Knisely KA0CZC@navix.net
Prairie Astronomy Club: http://www.prairieastronomyclub.org
Hyde Memorial Observatory: http://www.hydeobservatory.info/
**********************************************
* Attend the 14th Annual NEBRASKA STAR PARTY *
* July 15th-20th, 2007, Merritt Reservoir *
* http://www.NebraskaStarParty.org *
**********************************************
|
| | |
Date: 06 May 2007 10:42:09
From: Paul Schlyter
Subject: Re: 4 inch reflector can't resolve Mars at all
|
In article <1178366419.072601.215400@p77g2000hsh.googlegroups.com >,
<wsnell01@hotmail.com > wrote:
> On May 5, 4:19 am, David Knisely <KA0...@navix.net> wrote:
>> Chris L. Peterson wrote:
>>>> Finally, off axis coma is not a significant issue with an 8" f/6 newt, even
>>>> >with wide-field eyepieces. In our 10" f/6 dob, we regularly experience
>>>> >great high-power views while allowing the target to drift completely across
>>>> >the field. I have never heard anyone else comment on coma when observing
>>>> >with a newtonian of focal ratio in the range of 6 or higher.
>>
>>> That's a sign of uncritical observing, plain and simple. In an
>>> uncorrected Newt, coma is significant. Its effect on the MTF is much
>>> more important than central obstruction, for instance. Anybody who is a
>>> good enough observer to see the difference in contrast between an
>>> obstructed and unobstructed system will find the effects of coma much
>>> more obvious.
>>
>> Unfortunately, coma is not usually the main problem in an 8 inch f/6.
>> The most common problem is usually outer field astigmatism which, in
>> most of the less-complex eyepiece designs, completely masks any coma
>> that is present. Many people report the astigmatic appearance of outer
>> field stars as "coma" when it really isn't. I had to use a
>> well-corrected wide field eyepiece (Meade "original" 14mm Ultrawide)
>> before I got to see "pure" coma in an f/6 scope. The Paracorr
>> noticeably reduced the coma present, but in an f/6, I would still have
>> to call the amount relatively small (especially when compared to the
>> coma seen in something like an f/4.5 scope). Clear skies to you.
> > --
>
> Neither coma nor astigmatism is a "problem" in an 8-inch f/6 Dob
> since, as a practical matter, there is no other telescope that can
> potentially provide the same light gathering, resolution and contrast
> or as stable a mount for such a low price.
In other words, you get what you pay for.... ;-)
But surely one should be able to see details on Mars with a 4" scope!
I've seen details on Mars with a 2.4" f/15 refractor I got as a kid.
> The main "problems" to
> solve WRT to scope itself are collimation (not difficult), smooth
> motion (easy to remedy), having an appropriate selection of eyepieces/
> Barlows, and of course allowing enough time for the scope to "cool
> down" after being brought outdoors.
>
> Beyond that, the beginning observer will need to train his eye to see
> detail and will need to be patient and persistent enough to be looking
> through the eyepiece when the unsteady atmosphere settles down from
> time to time.
Very true.... with that 2.4" refractor I got as a kid, I was unable
to see any details on Mars during the 1963 and 1965 oppositions. Not
until the 1967 opposition I was able to see Syrtis Major, Sinus
Meridiani and a few other of the largest albedo features on Mars,
with that instrument.
--
----------------------------------------------------------------
Paul Schlyter, Grev Turegatan 40, SE-114 38 Stockholm, SWEDEN
e-mail: pausch at stockholm dot bostream dot se
WWW: http://stjarnhimlen.se/
|
| |
Date: 04 May 2007 09:38:32
From: laura halliday
Subject: Re: 4 inch reflector can't resolve Mars at all
|
On May 4, 7:19 am, Bullseye <b...@ei.com > wrote:
> On Fri, 4 May 2007 06:26:34 -0400, "Joe S." <non...@nosuch.net> wrote:
> >Collimating a Dob is easy. Here's my experiences with my XT-8:
> >http://www.schlatter.org/Dad/Astronomy/collimate.htm
>
> >Hope you find something useful.
>
> >Visit the Orion website and check out their Dobs -- I have an XT-12
> >Intelliscope. I use the handheld computer about 1/3 of the time, mostly
> >just starhop but the computer is nice to have.
>
> >When Mars does get into position for better viewing, you should be able to
> >make out the polar ice caps -- the planet will be a small orange ball but
> >you can see white on top and bottom -- not spectacular but clearly there.
>
> By better position I assume you mean December's opposition? Will there
> be any dark markings? How about from now till then?
Don't bother with Mars for a while yet. Practice your observing
skills on Saturn and Jupiter. The prime Mars season is a couple
of months either side of opposition; outside of that time, there
really is very little to see. You can watch Mars move across the
sky and get bigger in the interim, but expecting to see surface
detail is just not realistic until October or November. At the
moment Mars is only slightly larger than Uranus in a telescope.
For the 2003 opposition I had my first decent view in late
May, observed Mars lots in late August and early September,
and declared diminishing returns at the end of October. YMMV.
The 2005 opposition was an exercise in frustration: higher
in the sky, a gorgeous new telescope to play with, and dismal
weather. The few views I got, though, were breath taking.
The weather prospects for 2007 are similarly bad. :-(
Laura Halliday VE7LDH "Que les nuages soient notre
Grid: CN89mg pied a terre..."
ICBM: 49 16.05 N 122 56.92 W - Hospital/Shafte
|
| | |
Date: 04 May 2007 18:32:58
From: Bullseye
Subject: Re: 4 inch reflector can't resolve Mars at all
|
On 4 May 2007 09:38:32 -0700, laura halliday <marsgal42@hotmail.com >
wrote:
>Don't bother with Mars for a while yet. Practice your observing
>skills on Saturn and Jupiter. The prime Mars season is a couple
>of months either side of opposition; outside of that time, there
>really is very little to see. You can watch Mars move across the
>sky and get bigger in the interim, but expecting to see surface
>detail is just not realistic until October or November. At the
>moment Mars is only slightly larger than Uranus in a telescope.
>
>For the 2003 opposition I had my first decent view in late
>May, observed Mars lots in late August and early September,
>and declared diminishing returns at the end of October. YMMV.
>
>The 2005 opposition was an exercise in frustration: higher
>in the sky, a gorgeous new telescope to play with, and dismal
>weather. The few views I got, though, were breath taking.
>
>The weather prospects for 2007 are similarly bad. :-(
>
>Laura Halliday VE7LDH "Que les nuages soient notre
>Grid: CN89mg pied a terre..."
>ICBM: 49 16.05 N 122 56.92 W - Hospital/Shafte
oh I see. What kind of scope do you have?
|
| |
Date: 04 May 2007 04:17:50
From: thad@thadlabs.com
Subject: Re: 4 inch reflector can't resolve Mars at all
|
On May 4, 4:06 am, "t...@thadlabs.com" <t...@thadlabs.com > wrote:
> > [...]
> > Someone in the Yahoo
> > group just pointed me to a LONG document on how to collimate it. I'm
> > gonna take your statement and agree that it can be collimated in
> > expert hands but it is more complicated than most other scopes,
>
> Hmmm, assuming you mean Yahoo's "BabyNexstar" group, I'll take a
> look there and see what's written. I wonder if any OTA changes have
> occurred in the past 4 years?
Well, that wasn't the correct group -- nothing really new there
concerning
collimation. And I was banned from the other related group for
harping
on all the GOTO flaws and tracking glitches so I can't check there.
Oh well, maybe the OTAs should be tossed into SF Bay for use as marine
habitats. :-)
|
| | |
Date: 04 May 2007 14:21:55
From: Bullseye
Subject: Re: 4 inch reflector can't resolve Mars at all
|
On 4 May 2007 04:17:50 -0700, "thad@thadlabs.com" <thad@thadlabs.com >
wrote:
>On May 4, 4:06 am, "t...@thadlabs.com" <t...@thadlabs.com> wrote:
>> > [...]
>> > Someone in the Yahoo
>> > group just pointed me to a LONG document on how to collimate it. I'm
>> > gonna take your statement and agree that it can be collimated in
>> > expert hands but it is more complicated than most other scopes,
>>
>> Hmmm, assuming you mean Yahoo's "BabyNexstar" group, I'll take a
>> look there and see what's written. I wonder if any OTA changes have
>> occurred in the past 4 years?
>
>Well, that wasn't the correct group -- nothing really new there
>concerning
>collimation. And I was banned from the other related group for
>harping
>on all the GOTO flaws and tracking glitches so I can't check there.
>
>Oh well, maybe the OTAs should be tossed into SF Bay for use as marine
>habitats. :-)
lol banned? That's kinda harsh. Yeah it's the Nexstar group with 6,000
members not the BabyNexstar one.
|
| |
Date: 04 May 2007 04:06:58
From: thad@thadlabs.com
Subject: Re: 4 inch reflector can't resolve Mars at all
|
On May 4, 1:09 am, Bullseye <b...@ei.com > wrote:
> On 3 May 2007 23:56:07 -0700, "t...@thadlabs.com" <t...@thadlabs.com>
> wrote:
> >[...]
> >I disagree. I bought two 114GT systems at Costco about 2 months before
> >the 2003 Mars opposition to have additional scopes out for my Mars
> >party
> >and the OTA is the most difficult to collimate and use of any OTA I've
> >ever
> >used. Ever. I ended up with 10 other scopes/mounts out instead.
>
> >To be fair, in skilled hands (e.g., mine :-) a good view can be
> >achieved,
> >but I quickly decided that if anyone so much as looked crosseyed at
> >the focuser it'd be out of service for the evening. The two OTAs are
> >in
> >a box and their GOTO mounts are in service for binoculars and cameras.
>
> >Some pix here:
>
> ><http://thadlabs.com/ASTRO/Projects/#114GT>
>
> Hey I bought that 114GT at Costco about a week before the opposition
> in 2003 :)
Ours are probably from the same batch! :-)
> That is very enlightening, cause I've heard from some
> people you can collimate it, while others say it is not good cause it
> has a built in barlow and short focal ratio.
It can be collimated and I did it using every trick I've learned using
Newts since the 1950s, but it was tedious and the focuser leaves
a lot to be desired which is why I didn't bring them out for the Mars
party -- just touching the focuser with its builtin relay lens
(Barlow)
was inviting frustration for people inexperienced with it.
> Someone in the Yahoo
> group just pointed me to a LONG document on how to collimate it. I'm
> gonna take your statement and agree that it can be collimated in
> expert hands but it is more complicated than most other scopes,
Hmmm, assuming you mean Yahoo's "BabyNexstar" group, I'll take a
look there and see what's written. I wonder if any OTA changes have
occurred in the past 4 years?
> and
> the best thing is just getting an 8" dob. Thanks.
You're welcome! As others have written in this thread, the Orion
Newts (or Dobs if mounted on an alt/az rocker platform) are
extremely easy to collimate and use and they now come with a
really decent Crayford focuser, much better than the original
rack&pinion focuser (which I replaced on mine using the Orion
#13039 which is now standard on their Newts and Dobs). If
you get the Orion you'll be happy.
|
| |
Date: 03 May 2007 23:56:07
From: thad@thadlabs.com
Subject: Re: 4 inch reflector can't resolve Mars at all
|
On May 3, 10:32 pm, Chris L Peterson <c...@alumni.caltech.edu > wrote:
> On Fri, 04 May 2007 05:24:58 GMT, Bullseye <b...@ei.com> wrote:
> >So no markings on Mars? I've decided I'm gonna get an 8 inch dob. The
> >114GT I've been told has a short focal ratio and built-in barlow which
> >is known for producing poor images.
>
> You've been told wrong.
I disagree. I bought two 114GT systems at Costco about 2 months before
the 2003 Mars opposition to have additional scopes out for my Mars
party
and the OTA is the most difficult to collimate and use of any OTA I've
ever
used. Ever. I ended up with 10 other scopes/mounts out instead.
To be fair, in skilled hands (e.g., mine :-) a good view can be
achieved,
but I quickly decided that if anyone so much as looked crosseyed at
the focuser it'd be out of service for the evening. The two OTAs are
in
a box and their GOTO mounts are in service for binoculars and cameras.
Some pix here:
<http://thadlabs.com/ASTRO/Projects/#114GT >
|
| | |
Date: 04 May 2007 08:09:13
From: Bullseye
Subject: Re: 4 inch reflector can't resolve Mars at all
|
On 3 May 2007 23:56:07 -0700, "thad@thadlabs.com" <thad@thadlabs.com >
wrote:
>On May 3, 10:32 pm, Chris L Peterson <c...@alumni.caltech.edu> wrote:
>> On Fri, 04 May 2007 05:24:58 GMT, Bullseye <b...@ei.com> wrote:
>> >So no markings on Mars? I've decided I'm gonna get an 8 inch dob. The
>> >114GT I've been told has a short focal ratio and built-in barlow which
>> >is known for producing poor images.
>>
>> You've been told wrong.
>
>I disagree. I bought two 114GT systems at Costco about 2 months before
>the 2003 Mars opposition to have additional scopes out for my Mars
>party
>and the OTA is the most difficult to collimate and use of any OTA I've
>ever
>used. Ever. I ended up with 10 other scopes/mounts out instead.
>
>To be fair, in skilled hands (e.g., mine :-) a good view can be
>achieved,
>but I quickly decided that if anyone so much as looked crosseyed at
>the focuser it'd be out of service for the evening. The two OTAs are
>in
>a box and their GOTO mounts are in service for binoculars and cameras.
>
>Some pix here:
>
><http://thadlabs.com/ASTRO/Projects/#114GT>
Hey I bought that 114GT at Costco about a week before the opposition
in 2003 :) That is very enlightening, cause I've heard from some
people you can collimate it, while others say it is not good cause it
has a built in barlow and short focal ratio. Someone in the Yahoo
group just pointed me to a LONG document on how to collimate it. I'm
gonna take your statement and agree that it can be collimated in
expert hands but it is more complicated than most other scopes, and
the best thing is just getting an 8" dob. Thanks.
|
| | | |
Date: 04 May 2007 06:26:34
From: Joe S.
Subject: Re: 4 inch reflector can't resolve Mars at all
|
"Bullseye" <bulls@ei.com > wrote in message
news:1bql331nlp68b65foad4mkkf6cc9qamrtv@4ax.com...
> On 3 May 2007 23:56:07 -0700, "thad@thadlabs.com" <thad@thadlabs.com>
> wrote:
>
>>On May 3, 10:32 pm, Chris L Peterson <c...@alumni.caltech.edu> wrote:
>>> On Fri, 04 May 2007 05:24:58 GMT, Bullseye <b...@ei.com> wrote:
>>> >So no markings on Mars? I've decided I'm gonna get an 8 inch dob. The
>>> >114GT I've been told has a short focal ratio and built-in barlow which
>>> >is known for producing poor images.
>>>
>>> You've been told wrong.
>>
>>I disagree. I bought two 114GT systems at Costco about 2 months before
>>the 2003 Mars opposition to have additional scopes out for my Mars
>>party
>>and the OTA is the most difficult to collimate and use of any OTA I've
>>ever
>>used. Ever. I ended up with 10 other scopes/mounts out instead.
>>
>>To be fair, in skilled hands (e.g., mine :-) a good view can be
>>achieved,
>>but I quickly decided that if anyone so much as looked crosseyed at
>>the focuser it'd be out of service for the evening. The two OTAs are
>>in
>>a box and their GOTO mounts are in service for binoculars and cameras.
>>
>>Some pix here:
>>
>><http://thadlabs.com/ASTRO/Projects/#114GT>
>
>
> Hey I bought that 114GT at Costco about a week before the opposition
> in 2003 :) That is very enlightening, cause I've heard from some
> people you can collimate it, while others say it is not good cause it
> has a built in barlow and short focal ratio. Someone in the Yahoo
> group just pointed me to a LONG document on how to collimate it. I'm
> gonna take your statement and agree that it can be collimated in
> expert hands but it is more complicated than most other scopes, and
> the best thing is just getting an 8" dob. Thanks.
Collimating a Dob is easy. Here's my experiences with my XT-8:
http://www.schlatter.org/Dad/Astronomy/collimate.htm
Hope you find something useful.
Visit the Orion website and check out their Dobs -- I have an XT-12
Intelliscope. I use the handheld computer about 1/3 of the time, mostly
just starhop but the computer is nice to have.
When Mars does get into position for better viewing, you should be able to
make out the polar ice caps -- the planet will be a small orange ball but
you can see white on top and bottom -- not spectacular but clearly there.
|
| | | | |
Date: 04 May 2007 14:19:25
From: Bullseye
Subject: Re: 4 inch reflector can't resolve Mars at all
|
On Fri, 4 May 2007 06:26:34 -0400, "Joe S." <noname@nosuch.net > wrote:
>Collimating a Dob is easy. Here's my experiences with my XT-8:
>http://www.schlatter.org/Dad/Astronomy/collimate.htm
>
>Hope you find something useful.
>
>Visit the Orion website and check out their Dobs -- I have an XT-12
>Intelliscope. I use the handheld computer about 1/3 of the time, mostly
>just starhop but the computer is nice to have.
>
>When Mars does get into position for better viewing, you should be able to
>make out the polar ice caps -- the planet will be a small orange ball but
>you can see white on top and bottom -- not spectacular but clearly there.
By better position I assume you mean December's opposition? Will there
be any dark markings? How about from now till then?
|
| |
Date: 03 May 2007 23:24:33
From: Ben
Subject: Re: 4 inch reflector can't resolve Mars at all
|
On May 4, 12:32 am, Chris L Peterson <c...@alumni.caltech.edu > wrote:
> On Fri, 04 May 2007 05:24:58 GMT, Bullseye <b...@ei.com> wrote:
> >So no markings on Mars? I've decided I'm gonna get an 8 inch dob. The
> >114GT I've been told has a short focal ratio and built-in barlow which
> >is known for producing poor images.
>
> You've been told wrong.
Yeah, give it a break. The rule of thumb regarding Mars is that
you can begin to resolve features when Mars reaches 10" in
diameter. That occurs on 6 Oct 07. Of course this requires
excellent conditions.
The opposition date is Dec 24.822213. However it is closest
(0.5893 au) on Dec 19.
Ben
|
| |
Date: 03 May 2007 16:54:39
From:
Subject: Re: 4 inch reflector can't resolve Mars at all
|
On May 2, 7:36 pm, "Starlord" <starl...@sidewalkastronomy.info > wrote:
> I would go for a single high power EP, they do much better that the barlowed
> ones do. I used my 4.8naggler EP during mars passing.
>
I tend to disagree. A good Barlow, such as a Televue, works very
well.. You also effectively double the number of eyepieces you have,
giving you more flexibility WRT magnification, longer FL eyepieces
tend to have better eye relief and eyepieces used alone just barely
get you into the magnfication range needed with the typical f/6 focal
ratio.
However, the real point is that if the OP isn't prepared for Mars'
upcoming apparition, about seven months away, he will have to wait
seven YEARS, or longer, for an apparition as good. It's better, I
think, that he try to hone his skills with a larger scope, rather than
try to figure out what's wrong with a much smaller scope that didn't
work well for him at the previous (and better) apparition.
|
| |
Date: 03 May 2007 10:45:08
From: thad@thadlabs.com
Subject: Re: 4 inch reflector can't resolve Mars at all
|
On May 3, 10:12 am, Bullseye <b...@ei.com > wrote:
> [...]
> When Mars does show up
> higher in the sky in a few months what will we be able to see? You say
> in the 2003 opposition you were able to see the polar caps and dark
> markings. When it's not so close to Earth what do people usually see
> in 4-8 inch scopes? I hope it's not just an orange ball :)
Should be able to discern polar cap(s) as (at least) a white spot(s),
but
IIRC Mars will only subtend 15 or 16 arcseconds max on Dec. 24.
|
| | |
Date: 04 May 2007 05:24:58
From: Bullseye
Subject: Re: 4 inch reflector can't resolve Mars at all
|
On 3 May 2007 10:45:08 -0700, "thad@thadlabs.com" <thad@thadlabs.com >
wrote:
>On May 3, 10:12 am, Bullseye <b...@ei.com> wrote:
>> [...]
>> When Mars does show up
>> higher in the sky in a few months what will we be able to see? You say
>> in the 2003 opposition you were able to see the polar caps and dark
>> markings. When it's not so close to Earth what do people usually see
>> in 4-8 inch scopes? I hope it's not just an orange ball :)
>
>Should be able to discern polar cap(s) as (at least) a white spot(s),
>but
>IIRC Mars will only subtend 15 or 16 arcseconds max on Dec. 24.
So no markings on Mars? I've decided I'm gonna get an 8 inch dob. The
114GT I've been told has a short focal ratio and built-in barlow which
is known for producing poor images.
|
| | | |
Date: 04 May 2007 05:32:08
From: Chris L Peterson
Subject: Re: 4 inch reflector can't resolve Mars at all
|
On Fri, 04 May 2007 05:24:58 GMT, Bullseye <bulls@ei.com > wrote:
>So no markings on Mars? I've decided I'm gonna get an 8 inch dob. The
>114GT I've been told has a short focal ratio and built-in barlow which
>is known for producing poor images.
You've been told wrong.
_________________________________________________
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com
|
| | | | |
Date: 04 May 2007 05:58:09
From: Bullseye
Subject: Re: 4 inch reflector can't resolve Mars at all
|
On Fri, 04 May 2007 05:32:08 GMT, Chris L Peterson
<clp@alumni.caltech.edu > wrote:
>On Fri, 04 May 2007 05:24:58 GMT, Bullseye <bulls@ei.com> wrote:
>
>>So no markings on Mars? I've decided I'm gonna get an 8 inch dob. The
>>114GT I've been told has a short focal ratio and built-in barlow which
>>is known for producing poor images.
>
>You've been told wrong.
>
>_________________________________________________
>
>Chris L Peterson
>Cloudbait Observatory
>http://www.cloudbait.com
Well this is someone from the more specific Nexstar Yahoo group who
might know a little more about the Nexstar line of scopes. Plus he has
an Observatory signature underneath his post just like you ;)
No really I've tried with this scope, I'm not wasting another spring
and summer with it.
|
| | | | | |
Date: 04 May 2007 13:41:48
From: Chris L Peterson
Subject: Re: 4 inch reflector can't resolve Mars at all
|
On Fri, 04 May 2007 05:58:09 GMT, Bullseye <bulls@ei.com > wrote:
>Well this is someone from the more specific Nexstar Yahoo group who
>might know a little more about the Nexstar line of scopes. Plus he has
>an Observatory signature underneath his post just like you ;)
>No really I've tried with this scope, I'm not wasting another spring
>and summer with it.
It is possible that your particular scope has some serious issue, but
from the description of the problems you've given, it's very likely that
the scope isn't the primary problem. There is nothing intrinsically
terrible about this model; plenty of people have been happy with it.
Certainly, there are better scopes, and there's nothing wrong with
considering one. But you've been given some good advice here to take
what you already have to a star party or someplace where others with
more experience can help out- both with the scope itself and possibly
with your expectations of performance.
A decent 8" Newt will outperform a 4" instrument for planetary viewing-
assuming of course that you've mastered precision collimation. Keep in
mind my earlier warning however: keeping a planet centered at high
magnification with a Dob can be a chore, and you do need to keep the
planet centered for the best view. Off axis, coma will quickly degrade
the image.
_________________________________________________
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com
|
| | | | | | |
Date: 04 May 2007 11:41:40
From: Dennis Woos
Subject: Re: 4 inch reflector can't resolve Mars at all
|
> A decent 8" Newt will outperform a 4" instrument for planetary viewing-
> assuming of course that you've mastered precision collimation. Keep in
> mind my earlier warning however: keeping a planet centered at high
> magnification with a Dob can be a chore, and you do need to keep the
> planet centered for the best view. Off axis, coma will quickly degrade
> the image.
I disagree with much of what you posted. First off, precision collimation
is not required for good views in an 8" f/6 newt, if what you mean by
"precision" takes more than the 60 seconds that I usually spend. An
accurate laser/barlow is certainly sufficient for high-power planetary
viewing, and there are other less expensive options that work just as well
if less convenient.
Secondly, tracking a dob at high power is, for many folks, not a problem.
Our club is planning on offering a scope building class, where we will use
commercial optics, spider and focuser and teach/help folks to build a 6" f/8
dob. We had the prototype at a small star party last week, and I was
heartened to see that folks with little/no experience readily tracked Saturn
at 200x (6mm 60degree Burgess Planetary). Everyone was very satisfied with
the way the scope moved - smoothly and intuitively. I think that this the
key - the quality of the bearings. I agree that the bearings on the Chinese
dobs are not perfect, and this includes the ones sold by Orion. I wish they
were better, as there is no reason why they shouldn't be. However, they are
easily fixed by anybody who is even a bit comfortable with hand tools.
Finally, off axis coma is not a significant issue with an 8" f/6 newt, even
with wide-field eyepieces. In our 10" f/6 dob, we regularly experience
great high-power views while allowing the target to drift completely across
the field. I have never heard anyone else comment on coma when observing
with a newtonian of focal ratio in the range of 6 or higher.
Dennis
|
| | | | | | | |
Date: 13 May 2007 04:16:06
From:
Subject: Re: 4 inch reflector can't resolve Mars at all
|
On May 12, 5:41 am, pau...@saaf.se (Paul Schlyter) wrote:
> In article <1178927950.515878.321...@e51g2000hsg.googlegroups.com>,
>
> <wsnel...@hotmail.com> wrote:
> > On May 11, 3:42 am, pau...@saaf.se (Paul Schlyter) wrote:
> >> In article <1178842877.144621.36...@e65g2000hsc.googlegroups.com>,
>
> >> <wsnel...@hotmail.com> wrote:
> >>> To obtain tracking with all but the smallest scopes often seems to
> >>> double the cost of the instrument, conservatively.
>
> >> It will probably double the cost even for the smallest scopes: try to
> >> buy a toy scope at some department store, then buy an equatorial mounting
> >> with a clock drive for that scope.... I don't think cost doubling is
> >> enough in that case.
>
> > Well, yeah, I suppose you could put a 50mm refractor on an
> > Astrophysics mount - or a Questar OTA on an EQ-1,
>
> You could do a lot of weird things of course. But will you be able to
> even find an equatorial mount, with tracking, which costs not much more
> than a 50mm refractor in a department store?
A Poncet table, built in the original form (S&T Jan. 1977) should do
the trick. A cheap synch motor/tangent arm would suffice as the
drive. Even 50mm scopes run $40 to $50 or more, if a tripod/mount is
included.
>
> > but in general an
> > equatorial mount seems to account for about half the cost of a -
> > typical- setup. The mount for a Dobsonian OTOH consists mostly of a
> > few square yards of plywood, even for the large scopes, i.e. an almost
> > miniscule cost in comparison to the tube assembly.
>
> You said: "To obtain tracking with all but the smallest scopes often seems
> to double the cost of the instrument". My argument was that to get tracking
> on one of those smallest scopes will more than double the cost of it.
The equatorial StarBlast w /drive is only 45% more expensive than the
alt-az StarBlast, and only 10% more w/o drive. Look at the Orion site
for other examples. In the smaller sizes, an equatorial mount isn't
much more complicated to build than an altazimuth, and the cost of
eyepieces, finders, focusers, spiders, etc., is a larger factor in the
cost of small scopes, compared to larger scopes, as it should be.
>
> > For a few examples, $500-$600 buys you a 10-inch Dob or a 5-inch
> > equatorial Mak; $900-$1000 buys a 12-inch Dob or a 6-inch equatorial
> > Mak. OTOH an 8-inch Dob is available for around $360, while an 8-inch
> > equatorial Newt w/drive will run well over $700.
>
> Of course your argument is valid in *some* cases! I was merely
> arguing against its claimed general validity.
My arguments are valid in most cases not just some cases, and usually
valid for the sort of scope/mount combinations that most amateurs
would consider buying or building.
>I could point to the
> Questar which costs several thousand in its 3.5" version. This is much
> more than your 12-inch Dob or 6-inch equatorial, so in that particular
> case "a smaller aperture is more expensive". But that's a very
> special, not a general, rule!
>
Everything about the Questar is more expensive and it is aimed at a
somewhat different market than the usual astro telescope. However, the
lowest priced Standard Questar seems to be only 40% more expensive
than the lowest priced Field Model and the cost to convert to convert
that Field to a Duplex adds about 80% to the cost, i.e. once again the
mount is less than half the cost in small apertures.
>
> >>> Or for the same outlay you might get about half the aperture with a
> >>> scope that tracks.
>
> >>> Comparing a clock-driven 4-inch with an 8-inch Dob, by the end of the
> >>> night, you will have seen more detail in the larger scope. No matter
> >>> how long you stare at the perfectly centered image in the smaller,
> >>> clock-driven, scope, you will not, ultimately see as much as you would
> >>> through the larger Dob.
>
> >> Doesn't the cost of a scope generally increase more than the aperture?
> >> So that a scope with twice the aperture will cost more than twice as
> >> much?
>
> >> Otherwise giant scopes would be quite affordable - so that instead of
> >> 25 people each buying an 8-inch scope of their own, they could instead
> >> join and together buy, say, the 200-inch Hale telescope. If 50 people
> >> joined, they could buy one of the Keck telescopes. Wouldn't that be
> >> something? ;-)
>
> >> Earlier I've heard estimates that the cost of a scope is apporimately
> >> proportional to something between the square and the cube of the aperture,
> >> and that sounds more reasonable to me. If the cost rises as the cube
> >> of the aperture, then some 125,000 instead of just 50 potential buyers
> >> of personal 8-inch scopes would have to join forces to afford the Keck.
>
> > Yes, again, the cost does seem to scale up exponentially with
> > aperture, but the cost of an equatorial mounts rises too, as carrying
> > capacity increases.
>
> So the equatorial tracking mount will probably be about as expensive as
> the rest of the scope, and adding an equatorial mount and tracking will
> probably double the cost of the scope for many common scope sizes.
>
> But since the cost of the scope rises faster than linearly with aperture,
> if you omit the eq. mount you can probably not get a scope with twice
> the aperture for the same cost. Perhaps 40-50% larger aperture, but
> not 100% larger. In some cases (like the ones you pointed to above) you
> could probably get twice the aperture, but not in general.
In the middle range of aperture, an equatorial mount w/drive will
usually be roughly equal to the cost of the OTA, although it can be
argued that this might result in an undersized mount. In that case
you might consider spending more on a sturdier mount and/or a Mak or
SCT(compact, lighter, more expensive for given aperture) instead of a
Newtonian (long and heavy.) You will probably end up with about half
the aperture of a comparably priced Dob as a result, especially if you
are seeking a rig as smooth and stable as the Dob. The OP's 4-inch
scope tracked Mars for about the same price as an XT-8, but its OTA
was short and light; try using that mount for a 6-inch f/6!
> Also, a Dob isn't merely "an equatorial with the eq. mount removed".
> The Dob tries to simplify the entire scope to keep the costs down.
> As a result, the Dob is most likely of lower quality than the OTA of
> the equatorial scope. And I'm not just talking about the optics here.
> Perhaps the tube of the Dob is less stable, or causes more thermal
> turbulence during the cooldown of the scope? Perhaps the focusing of
> the Dob runs less smoothly? Perhaps the finder scope of the Dob is of
> lower quality, or even absent? There are many ways you could cut down
> the cost of a product - you do get what you pay for.
The XT-8 has a 50mm finder, 2-inch focuser, Plossl eyepieces, a steel
tube, a spider and mirror cell that look fine. Overall the OTA looks
comparable to Orion's 8-inch f/5 equatorials.
> > >> "But giant scopes also have an observatory built around them!", I hear
> >> you object. True, but people buy personal observatories around their
> >> 8-inch scopes too. And the cost of buildings will also increase
> >> faster than their physical size.
>
> > I don't get your point WRT to observatories, but a very large scope
> > might no longer be portable, so, yes, you will probably need an
> > observatory.
>
> Very large scopes must have an observatory: they're not portable but
> they still need shelter against bad weather. And I thought it was
> unfair to compare the cost of a very large scope with observatory with
> a much smaller scope without an observatory. That's how the
> observatory entered the discussion....
YOU brought up the idea of an observatory; I'm not even factoring it
in WRT cost. But if your scope is so large that you really do need to
build an observatory for it, it certainly seems fair to include that
in the costs
|
| | | | | | | |
Date: 11 May 2007 16:59:10
From:
Subject: Re: 4 inch reflector can't resolve Mars at all
|
On May 11, 3:42 am, pau...@saaf.se (Paul Schlyter) wrote:
> In article <1178842877.144621.36...@e65g2000hsc.googlegroups.com>,
>
> <wsnel...@hotmail.com> wrote:
> > To obtain tracking with all but the smallest scopes often seems to
> > double the cost of the instrument, conservatively.
>
> It will probably double the cost even for the smallest scopes: try to
> buy a toy scope at some department store, then buy an equatorial mounting
> with a clock drive for that scope.... I don't think cost doubling is
> enough in that case.
Well, yeah, I suppose you could put a 50mm refractor on an
Astrophysics mount - or a Questar OTA on an EQ-1, but in general an
equatorial mount seems to account for about half the cost of a -
typical- setup. The mount for a Dobsonian OTOH consists mostly of a
few square yards of plywood, even for the large scopes, i.e. an almost
miniscule cost in comparison to the tube assembly.
For a few examples, $500-$600 buys you a 10-inch Dob or a 5-inch
equatorial Mak; $900-$1000 buys a 12-inch Dob or a 6-inch equatorial
Mak. OTOH an 8-inch Dob is available for around $360, while an 8-inch
equatorial Newt w/drive will run well over $700.
> > Or for the same outlay you might get about half the aperture with a
> > scope that tracks.
>
> > Comparing a clock-driven 4-inch with an 8-inch Dob, by the end of the
> > night, you will have seen more detail in the larger scope. No matter
> > how long you stare at the perfectly centered image in the smaller,
> > clock-driven, scope, you will not, ultimately see as much as you would
> > through the larger Dob.
>
> Doesn't the cost of a scope generally increase more than the aperture?
> So that a scope with twice the aperture will cost more than twice as
> much?
>
> Otherwise giant scopes would be quite affordable - so that instead of
> 25 people each buying an 8-inch scope of their own, they could instead
> join and together buy, say, the 200-inch Hale telescope. If 50 people
> joined, they could buy one of the Keck telescopes. Wouldn't that be
> something? ;-)
>
> Earlier I've heard estimates that the cost of a scope is apporimately
> proportional to something between the square and the cube of the aperture,
> and that sounds more reasonable to me. If the cost rises as the cube
> of the aperture, then some 125,000 instead of just 50 potential buyers
> of personal 8-inch scopes would have to join forces to afford the Keck.
Yes, again, the cost does seem to scale up exponentially with
aperture, but the cost of an equatorial mounts rises too, as carrying
capacity increases.
> "But giant scopes also have an observatory built around them!", I hear
> you object. True, but people buy personal observatories around their
> 8-inch scopes too. And the cost of buildings will also increase
> faster than their physical size.
>
I don't get your point WRT to observatories, but a very large scope
might no longer be portable, so, yes, you will probably need an
observatory.
|
| | | | | | | | |
Date: 12 May 2007 09:41:54
From: Paul Schlyter
Subject: Re: 4 inch reflector can't resolve Mars at all
|
In article <1178927950.515878.321920@e51g2000hsg.googlegroups.com >,
<wsnell01@hotmail.com > wrote:
> On May 11, 3:42 am, pau...@saaf.se (Paul Schlyter) wrote:
>> In article <1178842877.144621.36...@e65g2000hsc.googlegroups.com>,
>>
>> <wsnel...@hotmail.com> wrote:
>>> To obtain tracking with all but the smallest scopes often seems to
>>> double the cost of the instrument, conservatively.
>>
>> It will probably double the cost even for the smallest scopes: try to
>> buy a toy scope at some department store, then buy an equatorial mounting
>> with a clock drive for that scope.... I don't think cost doubling is
>> enough in that case.
>
> Well, yeah, I suppose you could put a 50mm refractor on an
> Astrophysics mount - or a Questar OTA on an EQ-1,
You could do a lot of weird things of course. But will you be able to
even find an equatorial mount, with tracking, which costs not much more
than a 50mm refractor in a department store?
> but in general an
> equatorial mount seems to account for about half the cost of a -
> typical- setup. The mount for a Dobsonian OTOH consists mostly of a
> few square yards of plywood, even for the large scopes, i.e. an almost
> miniscule cost in comparison to the tube assembly.
You said: "To obtain tracking with all but the smallest scopes often seems
to double the cost of the instrument". My argument was that to get tracking
on one of those smallest scopes will more than double the cost of it.
> For a few examples, $500-$600 buys you a 10-inch Dob or a 5-inch
> equatorial Mak; $900-$1000 buys a 12-inch Dob or a 6-inch equatorial
> Mak. OTOH an 8-inch Dob is available for around $360, while an 8-inch
> equatorial Newt w/drive will run well over $700.
Of course your argument is valid in *some* cases! I was merely
arguing against its claimed general validity. I could point to the
Questar which costs several thousand in its 3.5" version. This is much
more than your 12-inch Dob or 6-inch equatorial, so in that particular
case "a smaller aperture is more expensive". But that's a very
special, not a general, rule!
>>> Or for the same outlay you might get about half the aperture with a
>>> scope that tracks.
>>
>>> Comparing a clock-driven 4-inch with an 8-inch Dob, by the end of the
>>> night, you will have seen more detail in the larger scope. No matter
>>> how long you stare at the perfectly centered image in the smaller,
>>> clock-driven, scope, you will not, ultimately see as much as you would
>>> through the larger Dob.
>>
>> Doesn't the cost of a scope generally increase more than the aperture?
>> So that a scope with twice the aperture will cost more than twice as
>> much?
>>
>> Otherwise giant scopes would be quite affordable - so that instead of
>> 25 people each buying an 8-inch scope of their own, they could instead
>> join and together buy, say, the 200-inch Hale telescope. If 50 people
>> joined, they could buy one of the Keck telescopes. Wouldn't that be
>> something? ;-)
>>
>> Earlier I've heard estimates that the cost of a scope is apporimately
>> proportional to something between the square and the cube of the aperture,
>> and that sounds more reasonable to me. If the cost rises as the cube
>> of the aperture, then some 125,000 instead of just 50 potential buyers
>> of personal 8-inch scopes would have to join forces to afford the Keck.
>
> Yes, again, the cost does seem to scale up exponentially with
> aperture, but the cost of an equatorial mounts rises too, as carrying
> capacity increases.
So the equatorial tracking mount will probably be about as expensive as
the rest of the scope, and adding an equatorial mount and tracking will
probably double the cost of the scope for many common scope sizes.
But since the cost of the scope rises faster than linearly with aperture,
if you omit the eq. mount you can probably not get a scope with twice
the aperture for the same cost. Perhaps 40-50% larger aperture, but
not 100% larger. In some cases (like the ones you pointed to above) you
could probably get twice the aperture, but not in general.
Also, a Dob isn't merely "an equatorial with the eq. mount removed".
The Dob tries to simplify the entire scope to keep the costs down.
As a result, the Dob is most likely of lower quality than the OTA of
the equatorial scope. And I'm not just talking about the optics here.
Perhaps the tube of the Dob is less stable, or causes more thermal
turbulence during the cooldown of the scope? Perhaps the focusing of
the Dob runs less smoothly? Perhaps the finder scope of the Dob is of
lower quality, or even absent? There are many ways you could cut down
the cost of a product - you do get what you pay for.
>> "But giant scopes also have an observatory built around them!", I hear
>> you object. True, but people buy personal observatories around their
>> 8-inch scopes too. And the cost of buildings will also increase
>> faster than their physical size.
>
> I don't get your point WRT to observatories, but a very large scope
> might no longer be portable, so, yes, you will probably need an
> observatory.
Very large scopes must have an observatory: they're not portable but
they still need shelter against bad weather. And I thought it was
unfair to compare the cost of a very large scope with observatory with
a much smaller scope without an observatory. That's how the
observatory entered the discussion....
--
----------------------------------------------------------------
Paul Schlyter, Grev Turegatan 40, SE-114 38 Stockholm, SWEDEN
e-mail: pausch at stockholm dot bostream dot se
WWW: http://stjarnhimlen.se/
|
| | | | | | | | | |
Date: 12 May 2007 08:20:07
From: Starlord
Subject: Re: 4 inch reflector can't resolve Mars at all
|
WRONG, I have been using Dobs since 1994 when I had my Orion 12.5 f4.8 dob
and only one or two times did I seen any air movement in the OTA. Since I
had to leve it in Hawaii I now own 3 dobs, a stargazer steve 4.25 f9, my
babylon 8 and the babylon 10 10 inch f5 dob and only once did I see anything
in the 10 inch one, but after I made some air holes that trouble has gone
away. Dods are made for a lot of viewing and mine have stood the test of
time. Somday I hope to made, build, or put toghter another 12.5 one.
--
The Lone Sidewalk Astronomer of Rosamond
Telescope Buyers FAQ
http://home.inreach.com/starlord
Sidewalk Astronomy
www.sidewalkastronomy.info
The Church of Eternity
http://home.inreach.com/starlord/church/Eternity.html
AD World
http://www.adworld.netfirms.com/
"Paul Schlyter" <pausch@saaf.se > wrote in message
news:f24203$1fft$1@merope.saaf.se...
> In article <1178927950.515878.321920@e51g2000hsg.googlegroups.com>,
> <wsnell01@hotmail.com> wrote:
>
> Of course your argument is valid in *some* cases! I was merely
> arguing against its claimed general validity. I could point to the
> Questar which costs several thousand in its 3.5" version. This is much
> more than your 12-inch Dob or 6-inch equatorial, so in that particular
> case "a smaller aperture is more expensive". But that's a very
> special, not a general, rule!
>
>
>
> So the equatorial tracking mount will probably be about as expensive as
> the rest of the scope, and adding an equatorial mount and tracking will
> probably double the cost of the scope for many common scope sizes.
>
> But since the cost of the scope rises faster than linearly with aperture,
> if you omit the eq. mount you can probably not get a scope with twice
> the aperture for the same cost. Perhaps 40-50% larger aperture, but
> not 100% larger. In some cases (like the ones you pointed to above) you
> could probably get twice the aperture, but not in general.
>
> Also, a Dob isn't merely "an equatorial with the eq. mount removed".
> The Dob tries to simplify the entire scope to keep the costs down.
> As a result, the Dob is most likely of lower quality than the OTA of
> the equatorial scope. And I'm not just talking about the optics here.
> Perhaps the tube of the Dob is less stable, or causes more thermal
> turbulence during the cooldown of the scope? Perhaps the focusing of
> the Dob runs less smoothly? Perhaps the finder scope of the Dob is of
> lower quality, or even absent? There are many ways you could cut down
> the cost of a product - you do get what you pay for.
>
>
>
> Very large scopes must have an observatory: they're not portable but
> they still need shelter against bad weather. And I thought it was
> unfair to compare the cost of a very large scope with observatory with
> a much smaller scope without an observatory. That's how the
> observatory entered the discussion....
>
|
| | | | | | | | | | |
Date: 12 May 2007 19:07:30
From:
Subject: Re: 4 inch reflector can't resolve Mars at all
|
Starlord wrote:
(snip)
Please don't top-post.
A: Because it messes up the order in which people normally read text.
Q: Why is top-posting such a bad thing?
A: Top-posting.
Q: What is the most annoying thing on Usenet?
-----------------------------------------------------------
"When thou enter a city, abide by its customs." -The Talmud
Quoting Style in Newsgroup Postings
http://www.xs4all.nl/%7ewijnands/nnq/nquote.html
How do I quote correctly in usenet?
http://www.netmeister.org/news/learn2quote2.html
Common Mistakes in Usenet Postings and How to Avoid Them
http://www.complang.tuwien.ac.at/anton/mail-news-errors.html#quoting
Bottom vs. top posting and quotation style on Usenet
http://www.cs.tut.fi/~jkorpela/usenet/brox.html
Why bottom-posting is better than top-posting
http://www.caliburn.nl/topposting.html
+What do you mean "my reply is upside-down"?
http://www.i-hate-computers.demon.co.uk/quote.html
Put an end to Outlook Express's messy quotes with this automated fix!
http://home.in.tum.de/~jain/software/oe-quotefix/
From (spit!) microsoft:
"When including text from a previous message in the thread,
trim it down to include only text pertinent to your response.
Your response should appear below the quoted information."
|
| | | | | | | | | | | |
Date: 12 May 2007 13:00:58
From: Starlord
Subject: Re: 4 inch reflector can't resolve Mars at all
|
I use outlook express and by default it set up the posting in that order and
that is the way I have posted even back in the days of my Atari TT030 in the
mid 90's.
Go fly a kite in a thunder storm.
Besides you go and hide yourself behind a stupid e-mail address. When you
fly that kite, make sure you've got wire in the string and you hold onto it
real tight.
--
The Lone Sidewalk Astronomer of Rosamond
Telescope Buyers FAQ
http://home.inreach.com/starlord
Sidewalk Astronomy
www.sidewalkastronomy.info
The Church of Eternity
http://home.inreach.com/starlord/church/Eternity.html
AD World
http://www.adworld.netfirms.com/
|
| | | | | | | | | | | | |
Date: 12 May 2007 20:36:13
From: Borked Pseudo Mailed
Subject: Re: I have 4 inch festering pustule on my arsehole
|
spammertard <starlord@sidewalkastronomy.info > shited his pantaloons:
>I use drugs out look my nappy headed ex whore prefelched gerbils and by default
>i tsetse his fly up my arsehole the pusting in that oder andy
> that i am dennis bishop i am a gobshite spammer stalker and barmy fawking
>plagiariser i copy the skytonight dot com astronomy site and spam it under the subject
>
> astro news
>
>without giving any credit to skytonight
> because i am a fawking spamming arsehole
>
>i plaway with my wagon i have gerbiled even back in the days of my first toy wagon when
> i was 48 fawking years old in 1998. i can count i am smartard i am shitetard
> i am dumb as a fawking rock
>
>Go open your fly up my kite in a thunder storm we can bugger and the neighbours
>can join in
>Besides i go and hide my gerbil tube up your arse you can hide your salami in my behind
> i have a stupid fawking e-mail address
>
> shitetard@reacharound.bugger.sod.orgy
>
> When you bugger my shitey arsehole make sure you dont get infected by the festering pustule
>that is growing out like a fawking pimple like a roid it is sore i have got a wire in the
>string for stitching up my distended sphincter but my gaping fawking arsehole is not real
>tight even for a 17 inch chubby telescope like yours
>
>
|
| | | | | | | | | | | | | |
Date: 13 May 2007 07:08:38
From: Hoots
Subject: Re: I have 4 inch festering pustule on my arsehole
|
Borked Pseudo Mailed wrote:
> spammertard <starlord@sidewalkastronomy.info> shited his pantaloons:
>> I use drugs out look my nappy headed ex whore prefelched gerbils and by default
>> i tsetse his fly up my arsehole the pusting in that oder andy
>> that i am dennis bishop i am a gobshite spammer stalker and barmy fawking
>> plagiariser i copy the skytonight dot com astronomy site and spam it under the subject
>>
>> astro news
>>
>> without giving any credit to skytonight
>> because i am a fawking spamming arsehole
>>
>> i plaway with my wagon i have gerbiled even back in the days of my first toy wagon when
>> i was 48 fawking years old in 1998. i can count i am smartard i am shitetard
>> i am dumb as a fawking rock
>>
>> Go open your fly up my kite in a thunder storm we can bugger and the neighbours
>> can join in
>> Besides i go and hide my gerbil tube up your arse you can hide your salami in my behind
>> i have a stupid fawking e-mail address
>>
>> shitetard@reacharound.bugger.sod.orgy
>>
>> When you bugger my shitey arsehole make sure you dont get infected by the festering pustule
>> that is growing out like a fawking pimple like a roid it is sore i have got a wire in the
>> string for stitching up my distended sphincter but my gaping fawking arsehole is not real
>> tight even for a 17 inch chubby telescope like yours
Now this one I understood.
Go figure.
|
| | | | | | | | | | | | |
Date: 12 May 2007 18:15:20
From: William R. Mattil
Subject: Re: 4 inch reflector can't resolve Mars at all
|
Starlord wrote:
> I use outlook express and by default it set up the posting in that order and
> that is the way I have posted even back in the days of my Atari TT030 in the
> mid 90's.
Dennis,
The default operation of Outlook express *can* actually be changed to
support conventional replies in-line. We all understand that you have
been doing it this way for a long time. But that still doesn't make it
the preferred method.
>
> Go fly a kite in a thunder storm.
> Besides you go and hide yourself behind a stupid e-mail address. When you
> fly that kite, make sure you've got wire in the string and you hold onto it
> real tight.
No Thanks. And I don't hide behind any handle or even a munged email
address.
The poster that you were replying to actually said "please" and wasn't
rude or otherwise obnoxious about it. So was this response really
warranted ?
Bill
|
| | | | | | | | | | | | | |
Date: 12 May 2007 17:16:53
From: Starlord
Subject: Re: 4 inch reflector can't resolve Mars at all
|
Well, I didn't see the "please" at all, but the way they where saying it,
didn't fit with me. I've looked over this program and the only I knd someway
to post below is to requote the whole message ontop first and I'm not the
only one this way I see others. This has not been a good week for me so you
could say they wrong thing was said at the wrond time, that ford I got is
now nothing but a junk pile which has me in the dumps.
And btw, even my paypal account is set up under my handle and I have neve
seen a rule where anyone couldn't use a handle as I have since the eary
1970's even offline.
--
The Lone Sidewalk Astronomer of Rosamond
Telescope Buyers FAQ
http://home.inreach.com/starlord
Sidewalk Astronomy
www.sidewalkastronomy.info
The Church of Eternity
http://home.inreach.com/starlord/church/Eternity.html
AD World
http://www.adworld.netfirms.com/
"William R. Mattil" <wrmattil@ix.netcom.com > wrote in message
news:2Ur1i.2553$UU.857@newssvr19.news.prodigy.net...
> Starlord wrote:
>> I use outlook express and by default it set up the posting in that order
>> and that is the way I have posted even back in the days of my Atari TT030
>> in the mid 90's.
>
> Dennis,
>
> The default operation of Outlook express *can* actually be changed to
> support conventional replies in-line. We all understand that you have been
> doing it this way for a long time. But that still doesn't make it the
> preferred method.
|
| | | | | | | | | | | | | | |
Date: 13 May 2007 01:13:32
From:
Subject: Re: 4 inch reflector can't resolve Mars at all
|
Starlord The Top-Poster wrote:
>Well, I didn't see the "please" at all, but the way they where saying it,
>didn't fit with me.
I wrote these words: "Please don't top-post." You didn't see one
third of what I wrote. I also don't see how I could have phrased
my request in such a way that it would "fit wit you" if a simple
"Please don't top-post" wasn't good enough.
>I've looked over this program and the only I knd someway
>to post below is to requote the whole message ontop first
The cursor is at the top so that you can navigate down
through the quoted material. trimming as you go, before
writing your reply at the bottom. Microsoft explained
this years ago:
Newsgroups: microsoft.public.windowsnt.*
Subject: [microsoft.public.windowsnt] Welcome - read this first!
Last-modified: 10/26/99
Copyright: (c) 1995-1999 Microsoft Corporation
Maintainer: essmvp@microsoft.com
When including text from a previous message
in the thread, trim it down to include only text
pertinent to your response. Your response
should appear below the quoted information.
In follow-ups, whether News or Mail, CUT
headers & signatures, PRUNE quotations,
and preserve order. That is to say, quote
above each part of your reply as much of the
earlier stuff as is needed to put the new material
in context, but no more; most readers will be able
to refer to the earlier article itself, if need be.
Never write on the same line as a quotation, except
in lists and notes; generally leave a wholly blank
line between. Do not quote the header or the
signature, unless it is relevant to do so.
>and I'm not the only one this way I see others.
In sci.astro.amateur? Or any other sct.* newsgroup?
Please provide a reference so that I may confirm your
claim.
>This has not been a good week for me so you could say
>they wrong thing was said at the wrond time, that ford
>I got is now nothing but a junk pile which has me in
>the dumps.
My sincere sympathy concerning your recent car troubles.
I am certainly willing to wait until things get better for
you before discussing how disruptive and annoying your
insistance on not following socialnorms is. How long
would you like me to wait?
>And btw, even my paypal account is set up under my handle
>and I have neve seen a rule where anyone couldn't use a
>handle as I have since the eary 1970's even offline.
Paypal troubles too! I hope that things get better for
you soon. Now this is just an idea, and I certainly don't
want to enrage you again, but would you perhaps be open to
the idea of posting like everyone else here? Who knows,
you might like it! It would certainly stop the criticism from
multiple annoyed people...
|
| | | | | | | | | | |
Date: 12 May 2007 16:06:26
From: Chris L Peterson
Subject: Re: 4 inch reflector can't resolve Mars at all
|
On Sat, 12 May 2007 08:20:07 -0700, "Starlord"
<starlord@sidewalkastronomy.info > wrote:
>WRONG, I have been using Dobs since 1994 when I had my Orion 12.5 f4.8 dob
>and only one or two times did I seen any air movement in the OTA. Since I
>had to leve it in Hawaii I now own 3 dobs, a stargazer steve 4.25 f9, my
>babylon 8 and the babylon 10 10 inch f5 dob and only once did I see anything
>in the 10 inch one, but after I made some air holes that trouble has gone
>away. Dods are made for a lot of viewing and mine have stood the test of
>time. Somday I hope to made, build, or put toghter another 12.5 one.
Any scope based on a long, mostly closed tube is going to be susceptible
to image degradation from air currents, especially a reflector design
(like a Newt) where the light traverses the tube more than once. People
looking for critical performance go to great care to minimize such
problems using carefully designed passive ventilation or active fans.
Paul's point was a good one: the Dob is typically a design that tries to
keep the cost in the optics. It is common for corners to be cut in terms
of the material and mechanical engineering. Therefore, many
off-the-shelf Dobs can show problems. This doesn't mean that there is
any fundamental problem with Dobs, nor that such problems aren't fairly
easily resolved. It is only recognizing the reality that an 8"-10" scope
that costs only a few hundred dollars probably isn't going to be
perfect.
_________________________________________________
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com
|
| | | | | | | | | | | |
Date: 12 May 2007 10:19:14
From: Starlord
Subject: Re: 4 inch reflector can't resolve Mars at all
|
My B8 has a mirror cell that allows air for move all around, the 10inch one
when I got it and as it's outside 98% of the time, I made a hole in the top
of the tube itself and then in the sheet of metal behind the mirror and this
allows air to move threw and guess what, since I made them last year even in
the warm summer time I am not bothered by air and I don;t have to worry
about mounting a fan and using batters either.
--
The Lone Sidewalk Astronomer of Rosamond
Telescope Buyers FAQ
http://home.inreach.com/starlord
Sidewalk Astronomy
www.sidewalkastronomy.info
The Church of Eternity
http://home.inreach.com/starlord/church/Eternity.html
AD World
http://www.adworld.netfirms.com/
"Chris L Peterson" <clp@alumni.caltech.edu > wrote in message
news:o1pb43p13mvr8l6fu823vrf9vpj2t9dt8c@4ax.com...
> Any scope based on a long, mostly closed tube is going to be susceptible
> to image degradation from air currents, especially a reflector design
> (like a Newt) where the light traverses the tube more than once. People
> looking for critical performance go to great care to minimize such
> problems using carefully designed passive ventilation or active fans.
>
|
| | | | | | | | | | | | |
Date: 12 May 2007 15:30:31
From: Borked Pseudo Mailed
Subject: Re: 4 inch wangdoodle buggers my sod wagon
|
stalkertard <starlord@sidewalkastronomy.info > felched:
>My babelshite ate my hose miropr cull hat al lows to bugger my bum air for movie all around
>bugger sods the 10inch one when I got it up my arse
>and arse my nancy teats pucker my tips i wear a b cup
> my wagon is bumside 98% of he and tim i mode a gerbil hole in the top of the tube
> itself and then in the shite of matt behind my trailer and his
>al lows a irt movie he wang puss hat since i mad heml asty ear sven in the arse
>he swarm sum buggers me all the fawking time
> i arm nut bot her shela by his pongy air an I dunce harvey to wory
>a butt mounting my biggest fan and using batters ether.
>
> i have a wagon it is red and sore i will oil up my wagon and hobble up to
>the star
>party for bugger sods they will bugger my wagon
>
>
>
>
>
>"Chris L Peterson" <clp@alumni.caltech.edu> wrote in message
>news:o1pb43p13mvr8l6fu823vrf9vpj2t9dt8c@4ax.com...
>> Any scope based on a long, mostly closed tube is going to be susceptible
>> to image degradation from air currents, especially a reflector design
>> (like a Newt) where the light traverses the tube more than once. People
>> looking for critical performance go to great care to minimize such
>> problems using carefully designed passive ventilation or active fans.
>>
|
| | | | | | | | | | | | | |
Date: 12 May 2007 20:16:21
From: Hoots
Subject: Re: 4 inch wangdoodle buggers my sod wagon
|
This one seems a bit difficult to comprehend.
Borked Pseudo Mailed wrote:
> stalkertard <starlord@sidewalkastronomy.info> felched:
>> My babelshite ate my hose miropr cull hat al lows to bugger my bum air for movie all around
>> bugger sods the 10inch one when I got it up my arse
>> and arse my nancy teats pucker my tips i wear a b cup
>> my wagon is bumside 98% of he and tim i mode a gerbil hole in the top of the tube
>> itself and then in the shite of matt behind my trailer and his
>> al lows a irt movie he wang puss hat since i mad heml asty ear sven in the arse
>> he swarm sum buggers me all the fawking time
>> i arm nut bot her shela by his pongy air an I dunce harvey to wory
>> a butt mounting my biggest fan and using batters ether.
>>
>> i have a wagon it is red and sore i will oil up my wagon and hobble up to
>> the star
>> party for bugger sods they will bugger my wagon
>>
>>
>>
>>
>>
>> "Chris L Peterson" <clp@alumni.caltech.edu> wrote in message
>> news:o1pb43p13mvr8l6fu823vrf9vpj2t9dt8c@4ax.com...
>>> Any scope based on a long, mostly closed tube is going to be susceptible
>>> to image degradation from air currents, especially a reflector design
>>> (like a Newt) where the light traverses the tube more than once. People
>>> looking for critical performance go to great care to minimize such
>>> problems using carefully designed passive ventilation or active fans.
>>>
|
| | | | | | | |
Date: 10 May 2007 17:21:17
From:
Subject: Re: 4 inch reflector can't resolve Mars at all
|
On May 10, 9:20 am, Chris L Peterson <c...@alumni.caltech.edu > wrote:
> On 10 May 2007 03:17:25 -0700, wsnel...@hotmail.com wrote:
>
> >Here is how a newbie might interpret this subthread:
>
> >USENET User 1: "Dobsonians don't track and at high power it's hard to
> >keep an object dead-center in the field of view, and if you don't,
> >coma will ruin the image."
>
> >USENET User 2: "That's not coma, that's astigmatism. I had to use a $
> >$$ eyepiece to get rid of the astigmatism, so that I could even see
> >the coma."
>
> >USENET Lurker/Newbie thinks to himself: "Wow, Dobsonians have so many
> >problems. No wonder they don't cost much. Maybe I should try
> >something else. Maybe this hobby is too expensive."
>
> Well, here's how a newbie _should_ interpret things:
>
> If I'm interested in critical, high power observation of planets, I need
> to be aware that a Dob doesn't track, and keeping the planet in the
> center of the field requires some effort. That may be more effort than
> I'd like to spend, and may indeed interfere with my ability to observe.
> I should consider evaluating a Dob for planetary observation before
> purchasing one.
>
> I should also be aware that typical uncorrected Newtonians display
> several off-axis aberrations, and while these are usually considered
> fairly minor, they are significant enough to visibly degrade planetary
> images as the target leaves the center of the field.
>
> Nothing here says that a newbie shouldn't buy a Dob, or that they have
> lots of problems. It only says that (like all scopes) they have
> limitations that should be considered by a potential purchaser, and that
> those limitations happen to be a little more obvious to planetary
> observers than to deep sky observers.
>
To obtain tracking with all but the smallest scopes often seems to
double the cost of the instrument, conservatively. Or for the same
outlay you might get about half the aperture with a scope that
tracks.
Comparing a clock-driven 4-inch with an 8-inch Dob, by the end of the
night, you will have seen more detail in the larger scope. No matter
how long you stare at the perfectly centered image in the smaller,
clock-driven, scope, you will not, ultimately see as much as you would
through the larger Dob.
|
| | | | | | | | |
Date: 11 May 2007 07:42:24
From: Paul Schlyter
Subject: Re: 4 inch reflector can't resolve Mars at all
|
In article <1178842877.144621.36130@e65g2000hsc.googlegroups.com >,
<wsnell01@hotmail.com > wrote:
> To obtain tracking with all but the smallest scopes often seems to
> double the cost of the instrument, conservatively.
It will probably double the cost even for the smallest scopes: try to
buy a toy scope at some department store, then buy an equatorial mounting
with a clock drive for that scope.... I don't think cost doubling is
enough in that case.
> Or for the same outlay you might get about half the aperture with a
> scope that tracks.
>
> Comparing a clock-driven 4-inch with an 8-inch Dob, by the end of the
> night, you will have seen more detail in the larger scope. No matter
> how long you stare at the perfectly centered image in the smaller,
> clock-driven, scope, you will not, ultimately see as much as you would
> through the larger Dob.
Doesn't the cost of a scope generally increase more than the aperture?
So that a scope with twice the aperture will cost more than twice as
much?
Otherwise giant scopes would be quite affordable - so that instead of
25 people each buying an 8-inch scope of their own, they could instead
join and together buy, say, the 200-inch Hale telescope. If 50 people
joined, they could buy one of the Keck telescopes. Wouldn't that be
something? ;-)
Earlier I've heard estimates that the cost of a scope is apporimately
proportional to something between the square and the cube of the aperture,
and that sounds more reasonable to me. If the cost rises as the cube
of the aperture, then some 125,000 instead of just 50 potential buyers
of personal 8-inch scopes would have to join forces to afford the Keck.
"But giant scopes also have an observatory built around them!", I hear
you object. True, but people buy personal observatories around their
8-inch scopes too. And the cost of buildings will also increase
faster than their physical size.
--
----------------------------------------------------------------
Paul Schlyter, Grev Turegatan 40, SE-114 38 Stockholm, SWEDEN
e-mail: pausch at stockholm dot bostream dot se
WWW: http://stjarnhimlen.se/
|
| | | | | | | | |
Date: 11 May 2007 00:33:35
From: Chris L Peterson
Subject: Re: 4 inch reflector can't resolve Mars at all
|
On 10 May 2007 17:21:17 -0700, wsnell01@hotmail.com wrote:
>To obtain tracking with all but the smallest scopes often seems to
>double the cost of the instrument, conservatively. Or for the same
>outlay you might get about half the aperture with a scope that
>tracks.
Often true, although a simple tracking platform for a Dob can be made
for a hundred bucks or so.
>Comparing a clock-driven 4-inch with an 8-inch Dob, by the end of the
>night, you will have seen more detail in the larger scope. No matter
>how long you stare at the perfectly centered image in the smaller,
>clock-driven, scope, you will not, ultimately see as much as you would
>through the larger Dob.
In principle, absolutely. In practice, maybe not. If you get frustrated
keeping a planet centered in a Dob (as I do), you will not spend as much
time, and you will likely not see as much. I know that I always see more
planetary detail in my 6" Mak (driven) and 12" LX200 than in my 8" Dob
(undriven) or my 12.5" Newt (with drive off). That isn't anything to do
with the optics, which is excellent in all cases, but simply with the
amount of attention that I find myself able to direct towards
observation. Part of this is the simple fact that planetary viewing is
difficult from my location, given the typical poor seeing. A good deal
of attention is required to pick out detail in brief moments of clarity.
_________________________________________________
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com
|
| | | | | | | |
Date: 04 May 2007 15:59:37
From: Chris L Peterson
Subject: Re: 4 inch reflector can't resolve Mars at all
|
On Fri, 4 May 2007 11:41:40 -0400, "Dennis Woos" <dpwoos@gmavt.net >
wrote:
>I disagree with much of what you posted. First off, precision collimation
>is not required for good views in an 8" f/6 newt, if what you mean by
>"precision" takes more than the 60 seconds that I usually spend. An
>accurate laser/barlow is certainly sufficient for high-power planetary
>viewing, and there are other less expensive options that work just as well
>if less convenient.
Many people with reasonable mechanical skills learn how to use a laser
collimator to achieve very good collimation. But my observation is that
many do not, which is why I suggested using a star as a test of
collimation, especially if the viewing plan includes planets at high
magnification. I don't see how anybody can disagree that very good
collimation is required if you want to get the best results when viewing
planets. It's easy enough to test- the tiniest amount of miscollimation
you can introduce noticeably reduces contrast.
>Secondly, tracking a dob at high power is, for many folks, not a problem...
That's true. But for others (myself included) it's a royal PITA. I did
say that this was only an issue for some people, and I think it's a very
fair warning to give anybody. The combination of no tracking and high
power observation is something to consider when looking at telescope
features.
>Finally, off axis coma is not a significant issue with an 8" f/6 newt, even
>with wide-field eyepieces. In our 10" f/6 dob, we regularly experience
>great high-power views while allowing the target to drift completely across
>the field. I have never heard anyone else comment on coma when observing
>with a newtonian of focal ratio in the range of 6 or higher.
That's a sign of uncritical observing, plain and simple. In an
uncorrected Newt, coma is significant. Its effect on the MTF is much
more important than central obstruction, for instance. Anybody who is a
good enough observer to see the difference in contrast between an
obstructed and unobstructed system will find the effects of coma much
more obvious.
Bottom line: with a Newt, if you want the best possible planetary views,
you'd better have near perfect collimation, and you'd better keep the
planet centered.
_________________________________________________
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com
|
| | | | | | | | |
Date: 05 May 2007 03:19:36
From: David Knisely
Subject: Re: 4 inch reflector can't resolve Mars at all
|
Chris L. Peterson wrote:
>> Finally, off axis coma is not a significant issue with an 8" f/6 newt, even
>> >with wide-field eyepieces. In our 10" f/6 dob, we regularly experience
>> >great high-power views while allowing the target to drift completely across
>> >the field. I have never heard anyone else comment on coma when observing
>> >with a newtonian of focal ratio in the range of 6 or higher.
>
> That's a sign of uncritical observing, plain and simple. In an
> uncorrected Newt, coma is significant. Its effect on the MTF is much
> more important than central obstruction, for instance. Anybody who is a
> good enough observer to see the difference in contrast between an
> obstructed and unobstructed system will find the effects of coma much
> more obvious.
Unfortunately, coma is not usually the main problem in an 8 inch f/6.
The most common problem is usually outer field astigmatism which, in
most of the less-complex eyepiece designs, completely masks any coma
that is present. Many people report the astigmatic appearance of outer
field stars as "coma" when it really isn't. I had to use a
well-corrected wide field eyepiece (Meade "original" 14mm Ultrawide)
before I got to see "pure" coma in an f/6 scope. The Paracorr
noticeably reduced the coma present, but in an f/6, I would still have
to call the amount relatively small (especially when compared to the
coma seen in something like an f/4.5 scope). Clear skies to you.
--
David W. Knisely KA0CZC@navix.net
Prairie Astronomy Club: http://www.prairieastronomyclub.org
Hyde Memorial Observatory: http://www.hydeobservatory.info/
**********************************************
* Attend the 14th Annual NEBRASKA STAR PARTY *
* July 15th-20th, 2007, Merritt Reservoir *
* http://www.NebraskaStarParty.org *
**********************************************
|
| | | | | | | | |
Date: 05 May 2007 01:41:36
From: Dennis Woos
Subject: Re: 4 inch reflector can't resolve Mars at all
|
"Chris L Peterson" <clp@alumni.caltech.edu > wrote in message
news:pglm33pjb4f51nrfmggrtkun4ejmuoohl1@4ax.com...
> On Fri, 4 May 2007 11:41:40 -0400, "Dennis Woos" <dpwoos@gmavt.net>
> wrote:
>
>>I disagree with much of what you posted. First off, precision collimation
>>is not required for good views in an 8" f/6 newt, if what you mean by
>>"precision" takes more than the 60 seconds that I usually spend. An
>>accurate laser/barlow is certainly sufficient for high-power planetary
>>viewing, and there are other less expensive options that work just as well
>>if less convenient.
>
> Many people with reasonable mechanical skills learn how to use a laser
> collimator to achieve very good collimation. But my observation is that
> many do not, which is why I suggested using a star as a test of
> collimation, especially if the viewing plan includes planets at high
> magnification. I don't see how anybody can disagree that very good
> collimation is required if you want to get the best results when viewing
> planets. It's easy enough to test- the tiniest amount of miscollimation
> you can introduce noticeably reduces contrast.
>
>
>>Secondly, tracking a dob at high power is, for many folks, not a
>>problem...
>
> That's true. But for others (myself included) it's a royal PITA. I did
> say that this was only an issue for some people, and I think it's a very
> fair warning to give anybody. The combination of no tracking and high
> power observation is something to consider when looking at telescope
> features.
>
>
>>Finally, off axis coma is not a significant issue with an 8" f/6 newt,
>>even
>>with wide-field eyepieces. In our 10" f/6 dob, we regularly experience
>>great high-power views while allowing the target to drift completely
>>across
>>the field. I have never heard anyone else comment on coma when observing
>>with a newtonian of focal ratio in the range of 6 or higher.
>
> That's a sign of uncritical observing, plain and simple. In an
> uncorrected Newt, coma is significant. Its effect on the MTF is much
> more important than central obstruction, for instance. Anybody who is a
> good enough observer to see the difference in contrast between an
> obstructed and unobstructed system will find the effects of coma much
> more obvious.
>
> Bottom line: with a Newt, if you want the best possible planetary views,
> you'd better have near perfect collimation, and you'd better keep the
> planet centered.
>
I am intrigued by your claim of visible coma in a relatively slow newtonian,
and I am certainly going to try and detect it and will also challenge other
folks in our club to do the same. At high powers I can't say that I
consistently detect any aberations in either our 6" f/8 or our 10" f/6 dobs.
I have looked at Nagler's performance graphs for his Paracorr here
(http://www.televue.com/engine/page.asp?ID=56 click on "see performance
graphs here", and it looks to me that at f/6, the coma is less than the airy
disk size across the field of a Nagler 4.8mm 82degree eyepiece. Given this,
it seems unreasonable to expect to detect coma in a 6mm 60degree eyepiece,
which is what I often use for viewing planets, and which is only 250x in our
10" f/6 dob.
My sons and I do regularly check our collimation with a star test, and we do
often tweak it as a result. However, I am not convinced that I would
normally notice the difference if we didn't. The seeing has to be pretty
good before we can get a view sufficient to do better than our barlowed
laser. We have found perfect (or as perfect as we can get) collimation
sometimes useful in splitting the most difficult doubles, for instance.
Again, I am interested in your claim, and I am going to try and detect a
noticeable improvement in planetary views after a more critical collimation.
Finally, telling a guy who couldn't see detail on Mars and who has only
gotten crappy views of Saturn that he has to worry about critical/perfect
collimation and coma seems somewhat unreasonable. A good newtonian of
reasonable focal ratio, in good collimation, should provide views that will
knock his socks off.
Dennis
|
| | | | | | | | |
Date: 04 May 2007 18:42:14
From: Paul Schlyter
Subject: Re: 4 inch reflector can't resolve Mars at all
|
In article <pglm33pjb4f51nrfmggrtkun4ejmuoohl1@4ax.com >,
Chris L Peterson <clp@alumni.caltech.edu > wrote:
> On Fri, 4 May 2007 11:41:40 -0400, "Dennis Woos" <dpwoos@gmavt.net>
> wrote:
>
>> I disagree with much of what you posted. First off, precision collimation
>> is not required for good views in an 8" f/6 newt, if what you mean by
>> "precision" takes more than the 60 seconds that I usually spend. An
>> accurate laser/barlow is certainly sufficient for high-power planetary
>> viewing, and there are other less expensive options that work just as well
>> if less convenient.
>
> Many people with reasonable mechanical skills learn how to use a laser
> collimator to achieve very good collimation. But my observation is that
> many do not, which is why I suggested using a star as a test of
> collimation, especially if the viewing plan includes planets at high
> magnification. I don't see how anybody can disagree that very good
> collimation is required if you want to get the best results when viewing
> planets. It's easy enough to test- the tiniest amount of miscollimation
> you can introduce noticeably reduces contrast.
There's really no disagreement between the two of you -- it's just a
difference in the desire for perfection. You want "the best" results,
while Dennis merely wants "good" results. Yes, there is a difference.
>> Finally, off axis coma is not a significant issue with an 8" f/6 newt, even
>> with wide-field eyepieces. In our 10" f/6 dob, we regularly experience
>> great high-power views while allowing the target to drift completely across
>> the field. I have never heard anyone else comment on coma when observing
>> with a newtonian of focal ratio in the range of 6 or higher.
>
> That's a sign of uncritical observing, plain and simple. In an
> uncorrected Newt, coma is significant. Its effect on the MTF is much
> more important than central obstruction, for instance. Anybody who is a
> good enough observer to see the difference in contrast between an
> obstructed and unobstructed system will find the effects of coma much
> more obvious.
Again, a difference in the desire of perfection....
> Bottom line: with a Newt, if you want the best possible planetary views,
He didn't - he merely wanted "good" views.... yes, one can enjoy something
even if there are imperfections.
> you'd better have near perfect collimation, and you'd better keep the
> planet centered.
--
----------------------------------------------------------------
Paul Schlyter, Grev Turegatan 40, SE-114 38 Stockholm, SWEDEN
e-mail: pausch at stockholm dot bostream dot se
WWW: http://stjarnhimlen.se/
|
| | | | | | | | | |
Date: 04 May 2007 14:19:04
From: Starlord
Subject: Re: 4 inch reflector can't resolve Mars at all
|
It's gone in my 8inch F8 Dob, never to be seen, and as I check it out before
it get loaded, it's alined dead on then and then once I get to the corner
some 4 miles away I check it again and it's right on dead center and every
star and or planet is the same size and shape that they show, but right now
that scope is being repaired and my 10inch f5 is doing the duty of being
taken up there and it's good, only trouble I've had with it is the 2inch ep
I got and then I findout it's a long foucs one and my scope is fase not ment
to work with each other so all my 1.25 ep's go for the ride.
--
The Lone Sidewalk Astronomer of Rosamond
Telescope Buyers FAQ
http://home.inreach.com/starlord
Sidewalk Astronomy
www.sidewalkastronomy.info
The Church of Eternity
http://home.inreach.com/starlord/church/Eternity.html
AD World
http://www.adworld.netfirms.com/
"Paul Schlyter" <pausch@saaf.se > wrote in message
Needs to use my good F8 dob, he'd blow his mind.
|
| | | | | | | | |
Date: 04 May 2007 10:10:52
From: Starlord
Subject: Re: 4 inch reflector can't resolve Mars at all
|
It's easy to lean good alinement and how to do it without a lazer, and many
times when I was thinnging of maybe getting one, I would look at my budget
and threw that idea right out the window, as I would need my money for other
reasons and because of that I can aline my scopes within a min afer putting
in the alinement ep and doing it even when I'm all the way up at the corner.
But I can do it at anyplace. but for the sidewalk astronomy deal later this
month I'll be taking my scope up on the red wagon with my ep's in my pocket
and will do everything up there once I get there. in the daylight. As my car
is dead right now and until I figure out what's wrong with it. right now I
stay inside as today we've got a 50mph winds blowing all over the place.
The Lone Sidewalk Astronomer of Rosamond
Telescope Buyers FAQ
http://home.inreach.com/starlord
Sidewalk Astronomy
www.sidewalkastronomy.info
The Church of Eternity
http://home.inreach.com/starlord/church/Eternity.html
AD World
http://www.adworld.netfirms.com/
"Chris L Peterson" <clp@alumni.caltech.edu > wrote in message
news:pglm33pjb4f51nrfmggrtkun4ejmuoohl1@4ax.com...
> On Fri, 4 May 2007 11:41:40 -0400, "Dennis Woos" <dpwoos@gmavt.net>
> wrote:
>
>>I disagree with much of what you posted. First off, precision collimation
>>is not required for good views in an 8" f/6 newt, if what you mean by
>>"precision" takes more than the 60 seconds that I usually spend. An
>>accurate laser/barlow is certainly sufficient for high-power planetary
>>viewing, and there are other less expensive options that work just as well
>>if less convenient.
>
> Many people with reasonable mechanical skills learn how to use a laser
> collimator to achieve very good collimation. But my observation is that
> many do not, which is why I suggested using a star as a test of
> collimation, especially if the viewing plan includes planets at high
> magnification. I don't see how anybody can disagree that very good
> collimation is required if you want to get the best results when viewing
> planets. It's easy enough to test- the tiniest amount of miscollimation
> you can introduce noticeably reduces contrast.
>
>
>>Secondly, tracking a dob at high power is, for many folks, not a
>>problem...
>
> That's true. But for others (myself included) it's a royal PITA. I did
> say that this was only an issue for some people, and I think it's a very
> fair warning to give anybody. The combination of no tracking and high
> power observation is something to consider when looking at telescope
> features.
>
>
>>Finally, off axis coma is not a significant issue with an 8" f/6 newt,
>>even
>>with wide-field eyepieces. In our 10" f/6 dob, we regularly experience
>>great high-power views while allowing the target to drift completely
>>across
>>the field. I have never heard anyone else comment on coma when observing
>>with a newtonian of focal ratio in the range of 6 or higher.
>
> That's a sign of uncritical observing, plain and simple. In an
> uncorrected Newt, coma is significant. Its effect on the MTF is much
> more important than central obstruction, for instance. Anybody who is a
> good enough observer to see the difference in contrast between an
> obstructed and unobstructed system will find the effects of coma much
> more obvious.
>
> Bottom line: with a Newt, if you want the best possible planetary views,
> you'd better have near perfect collimation, and you'd better keep the
> planet centered.
>
> _________________________________________________
>
> Chris L Peterson
> Cloudbait Observatory
> http://www.cloudbait.com
|
| | | | | | | | | |
Date: 04 May 2007 17:31:31
From: Chris L Peterson
Subject: Re: 4 inch reflector can't resolve Mars at all
|
On Fri, 4 May 2007 10:10:52 -0700, "Starlord"
<starlord@sidewalkastronomy.info > wrote:
>It's easy to lean good alinement and how to do it without a lazer...
Certainly, and I didn't mean to suggest that a laser is required for
collimation. It is a very effective way to get good collimation quickly,
however.
>As my car
>is dead right now and until I figure out what's wrong with it. right now I
>stay inside as today we've got a 50mph winds blowing all over the place.
In my experience, 50 mph winds are usually worse than bad collimation
when it comes to critical observing <g >.
_________________________________________________
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com
|
| | | | | | | | | | |
Date: 04 May 2007 14:10:10
From: Starlord
Subject: Re: 4 inch reflector can't resolve Mars at all
|
I can't even work on old B8 because of the winds, we've had gusts hit over
65mph at times I looked out at my garden and it's all flying dust.
Thankfully my two scopes I have that are useable are on my front porch and
safe from the weens which the weather man says are going to be worst
saterday too. can't ever walk to the store with wagon for a load of needed
stuff because the winds blasting everything.
almost like standing on mars in a dust storm.
--
The Lone Sidewalk Astronomer of Rosamond
Telescope Buyers FAQ
http://home.inreach.com/starlord
Sidewalk Astronomy
www.sidewalkastronomy.info
The Church of Eternity
http://home.inreach.com/starlord/church/Eternity.html
AD World
http://www.adworld.netfirms.com/
"Chris L Peterson" <clp@alumni.caltech.edu > wrote in message
news:9arm33p86cjso1a0lg3la73n7s2pt7lkec@4ax.com...
> On Fri, 4 May 2007 10:10:52 -0700, "Starlord"
> <starlord@sidewalkastronomy.info> wrote:
>
>>It's easy to lean good alinement and how to do it without a lazer...
>
> Certainly, and I didn't mean to suggest that a laser is required for
> collimation. It is a very effective way to get good collimation quickly,
> however.
>
>>As my car
>>is dead right now and until I figure out what's wrong with it. right now I
>>stay inside as today we've got a 50mph winds blowing all over the place.
>
> In my experience, 50 mph winds are usually worse than bad collimation
> when it comes to critical observing <g>.
>
> _________________________________________________
>
> Chris L Peterson
> Cloudbait Observatory
> http://www.cloudbait.com
|
| | | | | | |
Date: 04 May 2007 08:23:15
From: Starlord
Subject: Re: 4 inch reflector can't resolve Mars at all
|
Off axis, coma will quickly degrade the image.
I had my 12.5 f4.8 orion in 94 to 97, then now I have my stargazer steve
4.25inch f9, Bablon 8 8inch f8, B10 which is 10inch f5 and you want to know
something? I have good field of views in the ep of each one, nice and flat
and zero como, that has been left back on the factory floor.
--
There are those who believe that life here, began out there, far across the
universe, with tribes of humans, who may have been the forefathers of the
Egyptians, or the Toltecs, or the Mayans. Some believe that they may yet be
brothers of man, who even now fight to survive, somewhere beyond the
heavens.
The Lone Sidewalk Astronomer of Rosamond
Telescope Buyers FAQ
http://home.inreach.com/starlord
Sidewalk Astronomy
www.sidewalkastronomy.info
The Church of Eternity
http://home.inreach.com/starlord/church/Eternity.html
AD World
http://www.adworld.netfirms.com/
"Chris L Peterson" <clp@alumni.caltech.edu > wrote in message
news:mbdm33peirgaasl5lc1s338loh52cuc8k6@4ax.com...
> On Fri, 04 May 2007 05:58:09 GMT, Bullseye <bulls@ei.com> wrote:
>
>>Well this is someone from the more specific Nexstar Yahoo group who
>>might know a little more about the Nexstar line of scopes. Plus he has
>>an Observatory signature underneath his post just like you ;)
>>No really I've tried with this scope, I'm not wasting another spring
>>and summer with it.
>
> It is possible that your particular scope has some serious issue, but
> from the description of the problems you've given, it's very likely that
> the scope isn't the primary problem. There is nothing intrinsically
> terrible about this model; plenty of people have been happy with it.
>
> Certainly, there are better scopes, and there's nothing wrong with
> considering one. But you've been given some good advice here to take
> what you already have to a star party or someplace where others with
> more experience can help out- both with the scope itself and possibly
> with your expectations of performance.
>
> A decent 8" Newt will outperform a 4" instrument for planetary viewing-
> assuming of course that you've mastered precision collimation. Keep in
> mind my earlier warning however: keeping a planet centered at high
> magnification with a Dob can be a chore, and you do need to keep the
> planet centered for the best view. Off axis, coma will quickly degrade
> the image.
>
> _________________________________________________
>
> Chris L Peterson
> Cloudbait Observatory
> http://www.cloudbait.com
|
| | | | | | |
Date: 04 May 2007 14:14:43
From: Bullseye
Subject: Re: 4 inch reflector can't resolve Mars at all
|
On Fri, 04 May 2007 13:41:48 GMT, Chris L Peterson
<clp@alumni.caltech.edu > wrote:
>On Fri, 04 May 2007 05:58:09 GMT, Bullseye <bulls@ei.com> wrote:
>
>>Well this is someone from the more specific Nexstar Yahoo group who
>>might know a little more about the Nexstar line of scopes. Plus he has
>>an Observatory signature underneath his post just like you ;)
>>No really I've tried with this scope, I'm not wasting another spring
>>and summer with it.
>
>It is possible that your particular scope has some serious issue, but
>from the description of the problems you've given, it's very likely that
>the scope isn't the primary problem. There is nothing intrinsically
>terrible about this model; plenty of people have been happy with it.
>
>Certainly, there are better scopes, and there's nothing wrong with
>considering one. But you've been given some good advice here to take
>what you already have to a star party or someplace where others with
>more experience can help out- both with the scope itself and possibly
>with your expectations of performance.
>
>A decent 8" Newt will outperform a 4" instrument for planetary viewing-
>assuming of course that you've mastered precision collimation. Keep in
>mind my earlier warning however: keeping a planet centered at high
>magnification with a Dob can be a chore, and you do need to keep the
>planet centered for the best view. Off axis, coma will quickly degrade
>the image.
>
>_________________________________________________
>
>Chris L Peterson
>Cloudbait Observatory
>http://www.cloudbait.com
hmm, you've got a point, might have to consider the Intelliscope.
Thanks for the suggestion. Also the moon would stay in view for just a
second.
|
| | | | | | | |
Date: 04 May 2007 18:42:14
From: Paul Schlyter
Subject: Re: 4 inch reflector can't resolve Mars at all
|
In article <fufm33t2tf8e30d0odckodgvaqb67m2nuu@4ax.com >,
Bullseye <bulls@ei.com > wrote:
> hmm, you've got a point, might have to consider the Intelliscope.
> Thanks for the suggestion. Also the moon would stay in view for just a
> second.
Hmmm .... you must be using a too high magnification! To make the Moon
and the other celestial bodies appear to sweep across your field of view
in just one second due to the Earth's rotation will require a magnification
of some 5,000 to 10,000 times....
Try to lower the magnification by about a factor of 50 or so !!! Using
an unguided scope with a magnification exceeding approx. 100x is
awkward!
;-)
--
----------------------------------------------------------------
Paul Schlyter, Grev Turegatan 40, SE-114 38 Stockholm, SWEDEN
e-mail: pausch at stockholm dot bostream dot se
WWW: http://stjarnhimlen.se/
|
| | | | | | | | |
Date: 04 May 2007 20:06:50
From: Bullseye
Subject: Re: 4 inch reflector can't resolve Mars at all
|
On Fri, 04 May 2007 18:42:14 GMT, pausch@saaf.se (Paul Schlyter)
wrote:
>In article <fufm33t2tf8e30d0odckodgvaqb67m2nuu@4ax.com>,
>Bullseye <bulls@ei.com> wrote:
>
>> hmm, you've got a point, might have to consider the Intelliscope.
>> Thanks for the suggestion. Also the moon would stay in view for just a
>> second.
>
>Hmmm .... you must be using a too high magnification! To make the Moon
>and the other celestial bodies appear to sweep across your field of view
>in just one second due to the Earth's rotation will require a magnification
>of some 5,000 to 10,000 times....
>
>Try to lower the magnification by about a factor of 50 or so !!! Using
>an unguided scope with a magnification exceeding approx. 100x is
>awkward!
>
>;-)
I was just kidding. I just agree I'll probably need an Intelliscope to
track the planets and moon with an 8 incher. You need to move your
scope when looking at the moon even with a 4 incher so I can imagine
it would go even faster in an 8 incher.
|
| | | | | | | | | |
Date: 05 May 2007 11:42:37
From: Paul Schlyter
Subject: Re: 4 inch reflector can't resolve Mars at all
|
In article <de4n339migs8f7i6nkkpm9gel21bu6cr58@4ax.com >,
Bullseye <bulls@ei.com > wrote:
> I was just kidding. I just agree I'll probably need an Intelliscope to
> track the planets and moon with an 8 incher.
You need a clock driven mount for that, not an Intelliscope....
> You need to move your scope when looking at the moon even with a 4 incher
> so I can imagine it would go even faster in an 8 incher.
This will depend on the magnification, not on the aperture. You can use
a lower magnification on an 8-inch than on a 4-inch if you like.
--
----------------------------------------------------------------
Paul Schlyter, Grev Turegatan 40, SE-114 38 Stockholm, SWEDEN
e-mail: pausch at stockholm dot bostream dot se
WWW: http://stjarnhimlen.se/
|
| | | | | | | | | |
Date: 04 May 2007 13:20:09
From: Jan Owen
Subject: Re: 4 inch reflector can't resolve Mars at all
|
"Bullseye" <bulls@ei.com > wrote in message
news:de4n339migs8f7i6nkkpm9gel21bu6cr58@4ax.com...
> On Fri, 04 May 2007 18:42:14 GMT, pausch@saaf.se (Paul Schlyter)
> wrote:
>
>>In article <fufm33t2tf8e30d0odckodgvaqb67m2nuu@4ax.com>,
>>Bullseye <bulls@ei.com> wrote:
>>
>>> hmm, you've got a point, might have to consider the Intelliscope.
>>> Thanks for the suggestion. Also the moon would stay in view for just a
>>> second.
>>
>>Hmmm .... you must be using a too high magnification! To make the Moon
>>and the other celestial bodies appear to sweep across your field of view
>>in just one second due to the Earth's rotation will require a
>>magnification
>>of some 5,000 to 10,000 times....
>>
>>Try to lower the magnification by about a factor of 50 or so !!! Using
>>an unguided scope with a magnification exceeding approx. 100x is
>>awkward!
>>
>>;-)
>
> I was just kidding. I just agree I'll probably need an Intelliscope to
> track the planets and moon with an 8 incher. You need to move your
> scope when looking at the moon even with a 4 incher so I can imagine
> it would go even faster in an 8 incher.
The Intelliscopes do NOT track objects. They help you FIND stuff quickly,
by directing you to their celestial coordinates via directional arrows in a
display... But you still provide the motion TO the object, and YOU keep the
object in the field while observing by moving the scope by hand...
--
Jan Owen
To reach me directly, remove the Z, if one appears in my e-mail address...
Latitude: 33.6
Longitude: -112.3
http://community.webshots.com/user/janowen21
|
| | | | | | | | | | |
Date: 04 May 2007 22:08:01
From: Bullseye
Subject: Re: 4 inch reflector can't resolve Mars at all
|
On Fri, 4 May 2007 13:20:09 -0700, "Jan Owen" <janowen1@cox.net >
wrote:
>The Intelliscopes do NOT track objects. They help you FIND stuff quickly,
>by directing you to their celestial coordinates via directional arrows in a
>display... But you still provide the motion TO the object, and YOU keep the
>object in the field while observing by moving the scope by hand...
>
>--
>Jan Owen
>
>To reach me directly, remove the Z, if one appears in my e-mail address...
>Latitude: 33.6
>Longitude: -112.3
>http://community.webshots.com/user/janowen21
ah, I was under the impression it tracked cause when I used my goto
114GT I would just keep pressing the right or left button to move the
motor left or right. I just thought I was doing it manually and hadn't
programmed it to track. I hadn't used it much. Is moving a dob by hand
as easy and precise as pressing a button to move the motor left or
right?
|
| | | | | | | | | | | |
Date: 04 May 2007 18:52:31
From: Jan Owen
Subject: Re: 4 inch reflector can't resolve Mars at all
|
"Bullseye" <bulls@ei.com > wrote in message
news:mhbn33tkduskq06sb9msg3ohc8fdlh9luo@4ax.com...
> On Fri, 4 May 2007 13:20:09 -0700, "Jan Owen" <janowen1@cox.net>
> wrote:
>
>>The Intelliscopes do NOT track objects. They help you FIND stuff quickly,
>>by directing you to their celestial coordinates via directional arrows in
>>a
>>display... But you still provide the motion TO the object, and YOU keep
>>the
>>object in the field while observing by moving the scope by hand...
>>
>>--
>>Jan Owen
>>
>>To reach me directly, remove the Z, if one appears in my e-mail address...
>>Latitude: 33.6
>>Longitude: -112.3
>>http://community.webshots.com/user/janowen21
>
>
> ah, I was under the impression it tracked cause when I used my goto
> 114GT I would just keep pressing the right or left button to move the
> motor left or right. I just thought I was doing it manually and hadn't
> programmed it to track. I hadn't used it much. Is moving a dob by hand
> as easy and precise as pressing a button to move the motor left or
> right?
Depends on the bearings...
Ebony star or Formica, running on Teflon pads, will deliver buttery smooth
movement in both axes, if that's what's there.
But a lot of today's scopes seem to want to skimp on costs, even if it's
just a few cents, and you end up with some sort of nylon pads on another
weird type of laminate...
People CALL them Dobsonians, but many of the scopes out there seem to want
to try to use some other bearing materials, and attempt to convince newbies
that their system is superior... It rarely is... And John Dobson would
probably GAG over some of the choices being made to save a few cents...
If you have a real Dob, running on Teflon and Ebony Star or Formica, you
will have a scope that moves smoothly, stops when you want it to, and has NO
backlash in it... It's relatively easy to track at high power (though an
equatorial platform WILL make life simpler, if more expensive, in this
regard).
So, at the risk of repeating myself, if you plan to spend a lot of time
observing at HIGH power, tracking IS a very
real help. So with a Dobsonian, an equatorial platform of some sort can be
a MAJOR plus, even though it CAN be a bit expensive...
Here's one system you may want to consider...
http://www.roundtableplatforms.com/
--
Jan Owen
To reach me directly, remove the Z, if one appears in my e-mail address...
Latitude: 33.6
Longitude: -112.3
http://community.webshots.com/user/janowen21
|
| | | | | | | | | | | | |
Date: 04 May 2007 19:07:21
From: Starlord
Subject: Re: 4 inch reflector can't resolve Mars at all
|
When I had my Orion 12.5 f4.8 dob over in Hawaii the base was the same stuff
they use for countertops and the hole rockerbox was that way, the 3 pads
started sticking, so I replaced them with magic sliders that where 2 times
as big and never had any troubles after that and even to today I work
stars,planets,moon, what ever is in the Dobson hole, it's not a hole to me
and my telrad.
--
The Lone Sidewalk Astronomer of Rosamond
Telescope Buyers FAQ
http://home.inreach.com/starlord
Sidewalk Astronomy
www.sidewalkastronomy.info
The Church of Eternity
http://home.inreach.com/starlord/church/Eternity.html
AD World
http://www.adworld.netfirms.com/
"Jan Owen" <janowen1@cox.net > wrote in message
news:ArR_h.273724$JN6.162640@newsfe17.phx...
> "Bullseye" <bulls@ei.com> wrote in message
> news:mhbn33tkduskq06sb9msg3ohc8fdlh9luo@4ax.com...
>> On Fri, 4 May 2007 13:20:09 -0700, "Jan Owen" <janowen1@cox.net>
>> wrote:
>>
>>>The Intelliscopes do NOT track objects. They help you FIND stuff
>>>quickly,
>>>by directing you to their celestial coordinates via directional arrows in
>>>a
>>>display... But you still provide the motion TO the object, and YOU keep
>>>the
>>>object in the field while observing by moving the scope by hand...
>>>
>>>--
>>>Jan Owen
>>>
>>>To reach me directly, remove the Z, if one appears in my e-mail
>>>address...
>>>Latitude: 33.6
>>>Longitude: -112.3
>>>http://community.webshots.com/user/janowen21
>>
>>
>> ah, I was under the impression it tracked cause when I used my goto
>> 114GT I would just keep pressing the right or left button to move the
>> motor left or right. I just thought I was doing it manually and hadn't
>> programmed it to track. I hadn't used it much. Is moving a dob by hand
>> as easy and precise as pressing a button to move the motor left or
>> right?
>
> Depends on the bearings...
>
> Ebony star or Formica, running on Teflon pads, will deliver buttery smooth
> movement in both axes, if that's what's there.
>
> But a lot of today's scopes seem to want to skimp on costs, even if it's
> just a few cents, and you end up with some sort of nylon pads on another
> weird type of laminate...
>
> People CALL them Dobsonians, but many of the scopes out there seem to want
> to try to use some other bearing materials, and attempt to convince
> newbies
> that their system is superior... It rarely is... And John Dobson would
> probably GAG over some of the choices being made to save a few cents...
>
> If you have a real Dob, running on Teflon and Ebony Star or Formica, you
> will have a scope that moves smoothly, stops when you want it to, and has
> NO
> backlash in it... It's relatively easy to track at high power (though an
> equatorial platform WILL make life simpler, if more expensive, in this
> regard).
>
> So, at the risk of repeating myself, if you plan to spend a lot of time
> observing at HIGH power, tracking IS a very
> real help. So with a Dobsonian, an equatorial platform of some sort can
> be
> a MAJOR plus, even though it CAN be a bit expensive...
>
> Here's one system you may want to consider...
> http://www.roundtableplatforms.com/
> --
> Jan Owen
>
> To reach me directly, remove the Z, if one appears in my e-mail address...
> Latitude: 33.6
> Longitude: -112.3
> http://community.webshots.com/user/janowen21
>
|
| | | | | | | | | | | | | |
Date: 04 May 2007 19:24:30
From: Jan Owen
Subject: Re: 4 inch reflector can't resolve Mars at all
|
"Starlord" <starlord@sidewalkastronomy.info > wrote in message
news:IOOdnTsTTtB6dabbnZ2dnUVZ_jednZ2d@inreach.com...
> When I had my Orion 12.5 f4.8 dob over in Hawaii the base was the same
> stuff they use for countertops and the hole rockerbox was that way, the 3
> pads started sticking, so I replaced them with magic sliders that where 2
> times as big and never had any troubles after that and even to today I
> work stars,planets,moon, what ever is in the Dobson hole, it's not a hole
> to me and my telrad.
> --
> The Lone Sidewalk Astronomer of Rosamond
> Telescope Buyers FAQ
> http://home.inreach.com/starlord
> Sidewalk Astronomy
> www.sidewalkastronomy.info
> The Church of Eternity
> http://home.inreach.com/starlord/church/Eternity.html
> AD World
> http://www.adworld.netfirms.com/
>
Guess what?
If you know how to size the Teflon bearings, you won't have problems...
Though, if you don't know how to size them you could still get lucky...
--
Jan Owen
To reach me directly, remove the Z, if one appears in my e-mail address...
Latitude: 33.6
Longitude: -112.3
http://community.webshots.com/user/janowen21
>
> "Jan Owen" <janowen1@cox.net> wrote in message
> news:ArR_h.273724$JN6.162640@newsfe17.phx...
>> "Bullseye" <bulls@ei.com> wrote in message
>> news:mhbn33tkduskq06sb9msg3ohc8fdlh9luo@4ax.com...
>>> On Fri, 4 May 2007 13:20:09 -0700, "Jan Owen" <janowen1@cox.net>
>>> wrote:
>>>
>>>>The Intelliscopes do NOT track objects. They help you FIND stuff
>>>>quickly,
>>>>by directing you to their celestial coordinates via directional arrows
>>>>in a
>>>>display... But you still provide the motion TO the object, and YOU keep
>>>>the
>>>>object in the field while observing by moving the scope by hand...
>>>>
>>>>--
>>>>Jan Owen
>>>>
>>>>To reach me directly, remove the Z, if one appears in my e-mail
>>>>address...
>>>>Latitude: 33.6
>>>>Longitude: -112.3
>>>>http://community.webshots.com/user/janowen21
>>>
>>>
>>> ah, I was under the impression it tracked cause when I used my goto
>>> 114GT I would just keep pressing the right or left button to move the
>>> motor left or right. I just thought I was doing it manually and hadn't
>>> programmed it to track. I hadn't used it much. Is moving a dob by hand
>>> as easy and precise as pressing a button to move the motor left or
>>> right?
>>
>> Depends on the bearings...
>>
>> Ebony star or Formica, running on Teflon pads, will deliver buttery
>> smooth
>> movement in both axes, if that's what's there.
>>
>> But a lot of today's scopes seem to want to skimp on costs, even if it's
>> just a few cents, and you end up with some sort of nylon pads on another
>> weird type of laminate...
>>
>> People CALL them Dobsonians, but many of the scopes out there seem to
>> want
>> to try to use some other bearing materials, and attempt to convince
>> newbies
>> that their system is superior... It rarely is... And John Dobson would
>> probably GAG over some of the choices being made to save a few cents...
>>
>> If you have a real Dob, running on Teflon and Ebony Star or Formica, you
>> will have a scope that moves smoothly, stops when you want it to, and has
>> NO
>> backlash in it... It's relatively easy to track at high power (though an
>> equatorial platform WILL make life simpler, if more expensive, in this
>> regard).
>>
>> So, at the risk of repeating myself, if you plan to spend a lot of time
>> observing at HIGH power, tracking IS a very
>> real help. So with a Dobsonian, an equatorial platform of some sort can
>> be
>> a MAJOR plus, even though it CAN be a bit expensive...
>>
>> Here's one system you may want to consider...
>> http://www.roundtableplatforms.com/
>> --
>> Jan Owen
>>
>> To reach me directly, remove the Z, if one appears in my e-mail
>> address...
>> Latitude: 33.6
>> Longitude: -112.3
>> http://community.webshots.com/user/janowen21
>>
>
>
|
| | | | | | | | | | | | | | |
Date: 04 May 2007 20:36:31
From: Starlord
Subject: Re: 4 inch reflector can't resolve Mars at all
|
these where not the side barings, they where 3 pads for the upper disk to
use to ride on the lower disk as base and for turning, I had used them for 6
months when they got sticky so I replaced the 3 small pads that had come
with the scope with 3 2inch wide magic sliders from k-mart and they worked
good.
--
The Lone Sidewalk Astronomer of Rosamond
Telescope Buyers FAQ
http://home.inreach.com/starlord
Sidewalk Astronomy
www.sidewalkastronomy.info
The Church of Eternity
http://home.inreach.com/starlord/church/Eternity.html
AD World
http://www.adworld.netfirms.com/
"Jan Owen" <janowen1@cox.net > wrote in message
news:yVR_h.274339$JN6.161889@newsfe17.phx...
> If you know how to size the Teflon bearings, you won't have problems...
> Though, if you don't know how to size them you could still get lucky...
>
> --
> Jan Owen
|
| |
Date: 03 May 2007 04:21:03
From: Joe S.
Subject: Re: 4 inch reflector can't resolve Mars at all
|
"Bullseye" <bulls@ei.com > wrote in message
news:mcvh33592uhm1eo7c4uh1ib2ejnqkhfvib@4ax.com...
>I have a Nexstar 114GT and it can give visuals of the moon nicely
> (most scopes can I think) but I can't see sqwat when I point to Mars.
> I pointed to it 1-2 years ago when it was all over the news that it
> was close to Earth, but all I could see was a pink little ball, no
> features at all. Also in Saturn all I could see is a tiny little dot
> with a tiny circle around it. I've centered the scope and adjusted it
> all the ways I'm supposed to to get the best image (I've forgotten the
> exact terms that are used since I've ditched astronomy for awhile),
> but trust me I did. I just want to sell this sucker and get a new one.
> Can anyone recommend the best 4 inch reflectors out there for less
> than $500? Or maybe a very good 8 inch dob for less than $500?
First, let's deal with Mars.
Don't know where you are, but, here in East Tennessee, Mars is rising around
0430 and the sun shows up around 0530. Thus, for the hour before Mars is
wiped out by the rising sun, the planet is low on the horizon. Objects that
are low on the horizon generally are not good targets if you are looking for
detail -- because -- the lower on the horizon, the more atmosphere you are
looking through, thus, the more degraded are seeing conditions. You really
need to wait a few months when Mars is higher in the sky at night.
Now, as for an 8-inch Dob. You can't go wrong with the Orion XT-8. I owned
one until Hurricane Katrina swept it away and I was delighted with it. In
2003, when Mars made its historically close approach to Earth, I saw the
polar ice caps and the dark markings on Mars with no difficulty, viewing
from a light-polluted urban location.
Check out the Orion website for the XT-8. You will find a basic XT-8 (the
"classic") and the Intelliscope version. The Intelliscope version adds over
$100 to the basic price PLUS you then buy the Intelliscope controller for
another $100 or so. You can get the Intelliscope version without the
handheld computer-- the Intelliscope version has the encoders built into the
base -- it works just like a normal Dob -- you can add the handheld computer
later to the Intelliscope version but, if you buy the basic
(non-Intelliscope version), you can't add Intelliscope later.
Here are the Orion Dobs -- note that the "classic" XT-8 is now $369.95 and
the XT-10 is $549.95.
http://www.telescope.com/jump.jsp?itemType=CATEGORY&itemID=9
At that rate, if you stay with the "classic" without the Intelliscope, you
could afford to go to the 10-incher. If you go with the Intelliscope model,
the XT-8 fits your $500.00 budget.
Here is a description of my XT-12
http://www.schlatter.org/Dad/Astronomy/XT%2012.htm
and the Intelliscope
http://www.schlatter.org/Dad/Astronomy/intelliscope%20page.htm
The XT-series (4.5, 6, 8, 10, and 12) are the same scopes, just different
aperture and different physical size and weight. You can pick up and carry
the 4.5, and 6 easily; the 8 is a handful but can be carried; if you're
young and in good shape you can carry the 10; don't even think about
carrying the 12.
|
| | |
Date: 04 May 2007 15:37:09
From: laura halliday
Subject: Re: 4 inch reflector can't resolve Mars at all
|
On May 4, 11:32 am, Bullseye <b...@ei.com > wrote:
> oh I see. What kind of scope do you have?
2003: Synta 4.7" f/8 achromat.
2005: Takahashi TOA-130.
The Synta is a *nice* scope (hint, hint), but the Tak
is even nicer. At 10 times the price it had better be. :-)
Laura Halliday VE7LDH "Que les nuages soient notre
Grid: CN89mg pied a terre..."
ICBM: 49 16.05 N 122 56.92 W - Hospital/Shafte
|
| | |
Date: 03 May 2007 17:12:42
From: Bullseye
Subject: Re: 4 inch reflector can't resolve Mars at all
|
On Thu, 3 May 2007 04:21:03 -0400, "Joe S." <noname@nosuch.net > wrote:
>
>"Bullseye" <bulls@ei.com> wrote in message
>news:mcvh33592uhm1eo7c4uh1ib2ejnqkhfvib@4ax.com...
>>I have a Nexstar 114GT and it can give visuals of the moon nicely
>> (most scopes can I think) but I can't see sqwat when I point to Mars.
>> I pointed to it 1-2 years ago when it was all over the news that it
>> was close to Earth, but all I could see was a pink little ball, no
>> features at all. Also in Saturn all I could see is a tiny little dot
>> with a tiny circle around it. I've centered the scope and adjusted it
>> all the ways I'm supposed to to get the best image (I've forgotten the
>> exact terms that are used since I've ditched astronomy for awhile),
>> but trust me I did. I just want to sell this sucker and get a new one.
>> Can anyone recommend the best 4 inch reflectors out there for less
>> than $500? Or maybe a very good 8 inch dob for less than $500?
>
>First, let's deal with Mars.
>
>Don't know where you are, but, here in East Tennessee, Mars is rising around
>0430 and the sun shows up around 0530. Thus, for the hour before Mars is
>wiped out by the rising sun, the planet is low on the horizon. Objects that
>are low on the horizon generally are not good targets if you are looking for
>detail -- because -- the lower on the horizon, the more atmosphere you are
>looking through, thus, the more degraded are seeing conditions. You really
>need to wait a few months when Mars is higher in the sky at night.
>
>Now, as for an 8-inch Dob. You can't go wrong with the Orion XT-8. I owned
>one until Hurricane Katrina swept it away and I was delighted with it. In
>2003, when Mars made its historically close approach to Earth, I saw the
>polar ice caps and the dark markings on Mars with no difficulty, viewing
>from a light-polluted urban location.
>
>Check out the Orion website for the XT-8. You will find a basic XT-8 (the
>"classic") and the Intelliscope version. The Intelliscope version adds over
>$100 to the basic price PLUS you then buy the Intelliscope controller for
>another $100 or so. You can get the Intelliscope version without the
>handheld computer-- the Intelliscope version has the encoders built into the
>base -- it works just like a normal Dob -- you can add the handheld computer
>later to the Intelliscope version but, if you buy the basic
>(non-Intelliscope version), you can't add Intelliscope later.
>
>Here are the Orion Dobs -- note that the "classic" XT-8 is now $369.95 and
>the XT-10 is $549.95.
>http://www.telescope.com/jump.jsp?itemType=CATEGORY&itemID=9
>At that rate, if you stay with the "classic" without the Intelliscope, you
>could afford to go to the 10-incher. If you go with the Intelliscope model,
>the XT-8 fits your $500.00 budget.
>
>Here is a description of my XT-12
>http://www.schlatter.org/Dad/Astronomy/XT%2012.htm
>and the Intelliscope
>http://www.schlatter.org/Dad/Astronomy/intelliscope%20page.htm
>
>The XT-series (4.5, 6, 8, 10, and 12) are the same scopes, just different
>aperture and different physical size and weight. You can pick up and carry
>the 4.5, and 6 easily; the 8 is a handful but can be carried; if you're
>young and in good shape you can carry the 10; don't even think about
>carrying the 12.
>
Sorry about your scope getting swept away. When Mars does show up
higher in the sky in a few months what will we be able to see? You say
in the 2003 opposition you were able to see the polar caps and dark
markings. When it's not so close to Earth what do people usually see
in 4-8 inch scopes? I hope it's not just an orange ball :)
|
| | | |
Date: 10 May 2007 05:32:11
From: Jim Klein
Subject: Re: 4 inch reflector can't resolve Mars at all
|
In the 59 opposition with perfect seeing in the California desert (<17
degrees F) we had an 8" f/6 with a 4mm on top of two barlows. Mars
filled half the field. You could practically read the signs on the
canals. It was a view of a life time.
The brain learns to see what it needs to see. Recent studies indicate
the eye pre-processes before it sends to the brain and observing
trains this pre-processor. It is not the same but it is a little like
pre-amps on a CCD chip before the readout is sent on.
This is like comparing a movie to the individual frames. The eye/brain
fills in and "sharpens" when the movie is run even if the individual
frames had some motion blur.
Lots of observing tunes the eye/brain to see what is there but what
the untrained eye overlooks.
Jim
Bullseye <bulls@ei.com > wrote:
>On Thu, 3 May 2007 04:21:03 -0400, "Joe S." <noname@nosuch.net> wrote:
>
>>
>>"Bullseye" <bulls@ei.com> wrote in message
>>news:mcvh33592uhm1eo7c4uh1ib2ejnqkhfvib@4ax.com...
>>>I have a Nexstar 114GT and it can give visuals of the moon nicely
>>> (most scopes can I think) but I can't see sqwat when I point to Mars.
>>> I pointed to it 1-2 years ago when it was all over the news that it
>>> was close to Earth, but all I could see was a pink little ball, no
>>> features at all. Also in Saturn all I could see is a tiny little dot
>>> with a tiny circle around it. I've centered the scope and adjusted it
>>> all the ways I'm supposed to to get the best image (I've forgotten the
>>> exact terms that are used since I've ditched astronomy for awhile),
>>> but trust me I did. I just want to sell this sucker and get a new one.
>>> Can anyone recommend the best 4 inch reflectors out there for less
>>> than $500? Or maybe a very good 8 inch dob for less than $500?
>>
>>First, let's deal with Mars.
>>
>>Don't know where you are, but, here in East Tennessee, Mars is rising around
>>0430 and the sun shows up around 0530. Thus, for the hour before Mars is
>>wiped out by the rising sun, the planet is low on the horizon. Objects that
>>are low on the horizon generally are not good targets if you are looking for
>>detail -- because -- the lower on the horizon, the more atmosphere you are
>>looking through, thus, the more degraded are seeing conditions. You really
>>need to wait a few months when Mars is higher in the sky at night.
>>
>>Now, as for an 8-inch Dob. You can't go wrong with the Orion XT-8. I owned
>>one until Hurricane Katrina swept it away and I was delighted with it. In
>>2003, when Mars made its historically close approach to Earth, I saw the
>>polar ice caps and the dark markings on Mars with no difficulty, viewing
>>from a light-polluted urban location.
>>
>>Check out the Orion website for the XT-8. You will find a basic XT-8 (the
>>"classic") and the Intelliscope version. The Intelliscope version adds over
>>$100 to the basic price PLUS you then buy the Intelliscope controller for
>>another $100 or so. You can get the Intelliscope version without the
>>handheld computer-- the Intelliscope version has the encoders built into the
>>base -- it works just like a normal Dob -- you can add the handheld computer
>>later to the Intelliscope version but, if you buy the basic
>>(non-Intelliscope version), you can't add Intelliscope later.
>>
>>Here are the Orion Dobs -- note that the "classic" XT-8 is now $369.95 and
>>the XT-10 is $549.95.
>>http://www.telescope.com/jump.jsp?itemType=CATEGORY&itemID=9
>>At that rate, if you stay with the "classic" without the Intelliscope, you
>>could afford to go to the 10-incher. If you go with the Intelliscope model,
>>the XT-8 fits your $500.00 budget.
>>
>>Here is a description of my XT-12
>>http://www.schlatter.org/Dad/Astronomy/XT%2012.htm
>>and the Intelliscope
>>http://www.schlatter.org/Dad/Astronomy/intelliscope%20page.htm
>>
>>The XT-series (4.5, 6, 8, 10, and 12) are the same scopes, just different
>>aperture and different physical size and weight. You can pick up and carry
>>the 4.5, and 6 easily; the 8 is a handful but can be carried; if you're
>>young and in good shape you can carry the 10; don't even think about
>>carrying the 12.
>>
>
>Sorry about your scope getting swept away. When Mars does show up
>higher in the sky in a few months what will we be able to see? You say
>in the 2003 opposition you were able to see the polar caps and dark
>markings. When it's not so close to Earth what do people usually see
>in 4-8 inch scopes? I hope it's not just an orange ball :)
James E. Klein
jameseklein@earthlink.net
Engineering Calculations
http://www.ecalculations.com
ecalculations@ecalculations.com
Engineering Calculations is the home of
the KDP-2 Optical Design Program
for Windows.
1-818-507-5706 (Voice and Fax)
1-818-823-4121
"KDP2, not quite easy enough for a Caveman to use" :-)
|
| | | | |
Date: 09 May 2007 22:38:47
From: Brian Tung
Subject: Re: 4 inch reflector can't resolve Mars at all
|
Jim Klein wrote:
> In the 59 opposition with perfect seeing in the California desert (<17
> degrees F) we had an 8" f/6 with a 4mm on top of two barlows. Mars
> filled half the field. You could practically read the signs on the
> canals. It was a view of a life time.
>
> The brain learns to see what it needs to see. Recent studies indicate
> the eye pre-processes before it sends to the brain and observing
> trains this pre-processor. It is not the same but it is a little like
> pre-amps on a CCD chip before the readout is sent on.
>
> This is like comparing a movie to the individual frames. The eye/brain
> fills in and "sharpens" when the movie is run even if the individual
> frames had some motion blur.
>
> Lots of observing tunes the eye/brain to see what is there but what
> the untrained eye overlooks.
That sword has two edges, though. As Percival Lowell inadvertently
demonstrated, lots of observing can also tune the eye/brain to see what
isn't there, either. The brain is very good at interpreting what the
eye sees; the cost of that is that it interprets noise almost as well as
it interprets signal. Since there's no way to tell beforehand what is
signal and what is noise when you're observing "at the limit," so to
speak, it is impossible to see all the true features at the limit, and
never the false ones. There will always be some false positives. One
must always be on guard against too readily believing what one sees.
Cross-checking observations against other confirming observations, and
against similar observations in other sessions, is an effective way to
minimize this problem, but it can never be completely eliminated.
--
Brian Tung <brian@isi.edu >
The Astronomy Corner at http://astro.isi.edu/
Unofficial C5+ Home Page at http://astro.isi.edu/c5plus/
The PleiadAtlas Home Page at http://astro.isi.edu/pleiadatlas/
My Own Personal FAQ (SAA) at http://astro.isi.edu/reference/faq.html
|
| |
Date: 03 May 2007 03:08:26
From: Curtis Croulet
Subject: Re: 4 inch reflector can't resolve Mars at all
|
>I have a Nexstar 114GT and it can give visuals of the moon nicely
> (most scopes can I think) but I can't see sqwat when I point to Mars.
> I pointed to it 1-2 years ago when it was all over the news that it
> was close to Earth, but all I could see was a pink little ball, no
> features at all. Also in Saturn all I could see is a tiny little dot
> with a tiny circle around it.
The others have made good suggestions -- making sure your scope is
collimated and even getting a bigger scope -- but keep in mind that Mars is
always a very challenging object. Many observers express disappointment.
Worse, right now Mars is only about 5 arc seconds in diameter. No scope, no
matter the aperture or optical quality, is going to show much. In December,
when it gets up to almost 16 arc seconds, it'll be better. But even then,
don't expect much. If you can see a polar cap and Syrtis Major during the
December opposition, then you should feel fortunate. It'll be 2018 before
we have a decent opposition again. As for Saturn, when I show it to the
public in good "seeing," I get one of two reactions: (1) "That looks like a
picture!" or (2) "It's so small!" Saturn *is* small. In addition, the
three planets that offer any hope of seeing detail (Mars, Jupiter, Saturn)
are much paler than juiced up HST photos suggest. You might experiment with
eyepiece filters (red or orange for Mars) to enhance contrast, but don't
expect to see much on Mars right now.
--
Curtis Croulet
Temecula, California
33°27'59"N, 117°05'53"W
|
| |
Date: 02 May 2007 19:59:36
From: W. H. Greer
Subject: Re: 4 inch reflector can't resolve Mars at all
|
On Wed, 02 May 2007, Bullseye wrote:
>I have a Nexstar 114GT and it can give visuals of the moon nicely
>(most scopes can I think) but I can't see sqwat when I point to Mars.
>I pointed to it 1-2 years ago when it was all over the news that it
>was close to Earth, but all I could see was a pink little ball, no
>features at all. Also in Saturn all I could see is a tiny little dot
>with a tiny circle around it.
What magnification(s) did you use?
How many times have you tried to observe each planet?
What was your average amount of eyepiece time per planetary session?
How was the seeing? (steady image, boiling image, something in
between, etc?
If you own fewer than five eyepieces, which eyepieces do you have
(design and focal length)?
What's the focal length of your telescope?
Did you attempt to sketch what you saw?
Did you check the scope's collimation prior to *each* observing
session?
Most planetary detail tends to be of much lower contrast than much
that's encountered in lunar observing. Not only must your telescope
be 'tweaked' to perfection; but you must also repeatedly (and rather
intensely) study a planet in order to develop 'an eye' for the details
specific to the given planet.
> I've centered the scope and adjusted it
>all the ways I'm supposed to to get the best image (I've forgotten the
>exact terms that are used since I've ditched astronomy for awhile),
>but trust me I did.
I also read your 2nd posting in this thread. You might benefit from
checking some on-line references on collimation. It may be necessary
for you to make adjustments to *both* mirrors -- not just the primary
mirror. A good on-line reference to start with is here:
http://home.earthlink.net/~8-h-haggis/observing/beginners.htm
From the above site there are many worthy links, including one for
collimation. It may prove helpful to do a web-search and study
several different sources on collimation. Collimation is important
enough to gain a *thorough* understanding of.
>I just want to sell this sucker and get a new one.
>Can anyone recommend the best 4 inch reflectors out there for less
>than $500? Or maybe a very good 8 inch dob for less than $500?
IMO it would be wise to master collimation *before* purchasing another
Newtonian. Otherwise you may find yourself in the same boat once
again. The alternative would be to go with a different type of
telescope for your next telescope.
Finally, most important of all: If at all possible find your nearest
astronomy club (or attend the nearest 'starparty') and share your
concerns with the people you meet there. It's *far* easier to resolve
situations such as yours in person, with your telescope on hand for
inspection.
--
Bill
Celestial Journeys
http://cejour.blogspot.com
|
| | |
Date: 03 May 2007 10:32:58
From: W. H. Greer
Subject: Re: 4 inch reflector can't resolve Mars at all
|
A follow-up:
In situations such as this there are a multitude of possibilities,
only some of which have been addressed. Similarly, some of the
possibilities mentioned may not be relevant to the difficulties at
hand. None of us are all-knowing. None of us are able to study the
planetary images formed by your telescope. We don't mean to insult
your experience, intelligence, etc. when we offer suggestions. Yet,
sometimes I feel that my words (as well as those of others) may appear
to be somewhat condescending when they are not meant to be.
So, without making any assumptions I offer a list of possibilities in
no particular order:
poor seeing conditions
inadequately collimated optics
poor optical quality (telescope and/or eyepieces)
observer inexperience
insufficient magnification
thermal effects inside the telescope
thermal effects near the telescope
Other possibilities exist; but in my opinion (which is not always
correct) the difficulty is likely due to one or more of the
possibilities listed above. A knowledgeable amateur in your area, if
one could be found, would be able to pin down the problem and perhaps
even provide a remedy.
I would suggest not purchasing a new telescope until the cause of your
current difficulty has been determined or until you've seen and looked
through a telescope that you know you would enjoy owning.
Meanwhile, don't give up on your current telescope. Use it at every
reasonable opportunity. Your telescope is *far* superior to the best
telescope that Galileo used! It's capable of showing you *much* more
than what can be seen with your eyes alone.
Concentrate more on what you can see and less on what you can't see.
Photographs, CCD images and sketches often enhance the contrast and
color (when present) of planetary features. Colors tend to be very
subtle when present. Contrast likewise tends to be very subtle --
like the shadings on a small section of egg shell.
--
Bill
|
| |
Date: 02 May 2007 18:29:18
From: Ben
Subject: Re: 4 inch reflector can't resolve Mars at all
|
On May 2, 7:30 pm, Phoon Hencman <H...@ican.net > wrote:
> On 2007-05-02 18:14:39 -0400, Chris L Peterson <c...@alumni.caltech.edu> said:
>
And remember, seeing conditions play an IMPORtANT part too.
During the 2005 opposition there were several large dust storms
on Mars and its atmosphere was too dustydirty to allow albedo
features to be resolved sharply.
I did 150 drawings of it for the "Grand Opposition of 2003" but
on the last one I didn't even get out my sketchpad.
Ben
|
| |
Date: 02 May 2007 16:09:52
From:
Subject: Re: 4 inch reflector can't resolve Mars at all
|
On May 2, 5:21 pm, Bullseye <b...@ei.com > wrote:
> I have a Nexstar 114GT and it can give visuals of the moon nicely
> (most scopes can I think) but I can't see sqwat when I point to Mars.
> I pointed to it 1-2 years ago when it was all over the news that it
> was close to Earth, but all I could see was a pink little ball, no
> features at all. Also in Saturn all I could see is a tiny little dot
> with a tiny circle around it. I've centered the scope and adjusted it
> all the ways I'm supposed to to get the best image (I've forgotten the
> exact terms that are used since I've ditched astronomy for awhile),
> but trust me I did. I just want to sell this sucker and get a new one.
> Can anyone recommend the best 4 inch reflectors out there for less
> than $500? Or maybe a very good 8 inch dob for less than $500?
Mars will be almost overhead for north temperate latitudes this
December, although less than 16 arc-sec in diameter, so get yourself a
bigger telescope ASAP. For $500 you should be able to get an 8-inch
Dob AND a good 3x Barlow (you will probably need one.) If you can
stretch the budget a couple of hundred dollars go for a 10-inch, but
don't delay your purchase too long. Make sure you have about 30x to
35x per inch of aperture.
Practice observing Jupiter and Saturn, so that you will be ready for
Mars.
|
| | |
Date: 02 May 2007 16:36:15
From: Starlord
Subject: Re: 4 inch reflector can't resolve Mars at all
|
I would go for a single high power EP, they do much better that the barlowed
ones do. I used my 4.8naggler EP during mars passing.
The Lone Sidewalk Astronomer of Rosamond
Telescope Buyers FAQ
http://home.inreach.com/starlord
Sidewalk Astronomy
www.sidewalkastronomy.info
The Church of Eternity
http://home.inreach.com/starlord/church/Eternity.html
AD World
http://www.adworld.netfirms.com/
<wsnell01@hotmail.com > wrote in message
news:1178147392.255259.289380@h2g2000hsg.googlegroups.com...
> On May 2, 5:21 pm, Bullseye <b...@ei.com> wrote:
>> I have a Nexstar 114GT and it can give visuals of the moon nicely
>> (most scopes can I think) but I can't see sqwat when I point to Mars.
>> I pointed to it 1-2 years ago when it was all over the news that it
>> was close to Earth, but all I could see was a pink little ball, no
>> features at all. Also in Saturn all I could see is a tiny little dot
>> with a tiny circle around it. I've centered the scope and adjusted it
>> all the ways I'm supposed to to get the best image (I've forgotten the
>> exact terms that are used since I've ditched astronomy for awhile),
>> but trust me I did. I just want to sell this sucker and get a new one.
>> Can anyone recommend the best 4 inch reflectors out there for less
>> than $500? Or maybe a very good 8 inch dob for less than $500?
>
> Mars will be almost overhead for north temperate latitudes this
> December, although less than 16 arc-sec in diameter, so get yourself a
> bigger telescope ASAP. For $500 you should be able to get an 8-inch
> Dob AND a good 3x Barlow (you will probably need one.) If you can
> stretch the budget a couple of hundred dollars go for a 10-inch, but
> don't delay your purchase too long. Make sure you have about 30x to
> 35x per inch of aperture.
>
> Practice observing Jupiter and Saturn, so that you will be ready for
> Mars.
>
|
| | | |
Date: 03 May 2007 00:04:32
From: Bullseye
Subject: Re: 4 inch reflector can't resolve Mars at all
|
On Wed, 2 May 2007 16:36:15 -0700, "Starlord"
<starlord@sidewalkastronomy.info > wrote:
>I would go for a single high power EP, they do much better that the barlowed
>ones do. I used my 4.8naggler EP during mars passing.
>
>
>The Lone Sidewalk Astronomer of Rosamond
>Telescope Buyers FAQ
>http://home.inreach.com/starlord
>Sidewalk Astronomy
>www.sidewalkastronomy.info
>The Church of Eternity
>http://home.inreach.com/starlord/church/Eternity.html
>AD World
>http://www.adworld.netfirms.com/
>
>
><wsnell01@hotmail.com> wrote in message
>news:1178147392.255259.289380@h2g2000hsg.googlegroups.com...
>> On May 2, 5:21 pm, Bullseye <b...@ei.com> wrote:
>>> I have a Nexstar 114GT and it can give visuals of the moon nicely
>>> (most scopes can I think) but I can't see sqwat when I point to Mars.
>>> I pointed to it 1-2 years ago when it was all over the news that it
>>> was close to Earth, but all I could see was a pink little ball, no
>>> features at all. Also in Saturn all I could see is a tiny little dot
>>> with a tiny circle around it. I've centered the scope and adjusted it
>>> all the ways I'm supposed to to get the best image (I've forgotten the
>>> exact terms that are used since I've ditched astronomy for awhile),
>>> but trust me I did. I just want to sell this sucker and get a new one.
>>> Can anyone recommend the best 4 inch reflectors out there for less
>>> than $500? Or maybe a very good 8 inch dob for less than $500?
>>
>> Mars will be almost overhead for north temperate latitudes this
>> December, although less than 16 arc-sec in diameter, so get yourself a
>> bigger telescope ASAP. For $500 you should be able to get an 8-inch
>> Dob AND a good 3x Barlow (you will probably need one.) If you can
>> stretch the budget a couple of hundred dollars go for a 10-inch, but
>> don't delay your purchase too long. Make sure you have about 30x to
>> 35x per inch of aperture.
>>
>> Practice observing Jupiter and Saturn, so that you will be ready for
>> Mars.
>>
That's the term I meant to use, "collimated". I had forgotten it
because it's been a long while. I tried collimating it the cheap way.
Taking one of those small black containers that hold a roll of film,
making a small hole in the middle. Sticking a small dot in the middle
of my mirror, and trying to align it with the screws. If that's not a
good way to do it then I'll have to buy one of those laser
collimators. But I'm also thinking about just getting one of the 8"
dobs. Thanks for your suggestions.
|
| | | | |
Date: 02 May 2007 20:07:36
From: Starlord
Subject: Re: 4 inch reflector can't resolve Mars at all
|
I aline ALL of my scopes using a 35mm film can(plastic) and I'd lay odds
that with me doing sidewalk astronomy it's just as good as a laszer one
which I don't need/
The Lone Sidewalk Astronomer of Rosamond
Telescope Buyers FAQ
http://home.inreach.com/starlord
Sidewalk Astronomy
www.sidewalkastronomy.info
The Church of Eternity
http://home.inreach.com/starlord/church/Eternity.html
AD World
http://www.adworld.netfirms.com/
"Bullseye" <bulls@ei.com > wrote in message
news:sf9i33td43ou8mkm9gb9qkl52pr5g1od4a@4ax.com...
> On Wed, 2 May 2007 16:36:15 -0700, "Starlord"
> <starlord@sidewalkastronomy.info> wrote:
>
>>I would go for a single high power EP, they do much better that the
>>barlowed
>>ones do. I used my 4.8naggler EP during mars passing.
>>
>>
>>The Lone Sidewalk Astronomer of Rosamond
>>Telescope Buyers FAQ
>>http://home.inreach.com/starlord
>>Sidewalk Astronomy
>>www.sidewalkastronomy.info
>>The Church of Eternity
>>http://home.inreach.com/starlord/church/Eternity.html
>>AD World
>>http://www.adworld.netfirms.com/
>>
>>
>><wsnell01@hotmail.com> wrote in message
>>news:1178147392.255259.289380@h2g2000hsg.googlegroups.com...
>>> On May 2, 5:21 pm, Bullseye <b...@ei.com> wrote:
>>>> I have a Nexstar 114GT and it can give visuals of the moon nicely
>>>> (most scopes can I think) but I can't see sqwat when I point to Mars.
>>>> I pointed to it 1-2 years ago when it was all over the news that it
>>>> was close to Earth, but all I could see was a pink little ball, no
>>>> features at all. Also in Saturn all I could see is a tiny little dot
>>>> with a tiny circle around it. I've centered the scope and adjusted it
>>>> all the ways I'm supposed to to get the best image (I've forgotten the
>>>> exact terms that are used since I've ditched astronomy for awhile),
>>>> but trust me I did. I just want to sell this sucker and get a new one.
>>>> Can anyone recommend the best 4 inch reflectors out there for less
>>>> than $500? Or maybe a very good 8 inch dob for less than $500?
>>>
>>> Mars will be almost overhead for north temperate latitudes this
>>> December, although less than 16 arc-sec in diameter, so get yourself a
>>> bigger telescope ASAP. For $500 you should be able to get an 8-inch
>>> Dob AND a good 3x Barlow (you will probably need one.) If you can
>>> stretch the budget a couple of hundred dollars go for a 10-inch, but
>>> don't delay your purchase too long. Make sure you have about 30x to
>>> 35x per inch of aperture.
>>>
>>> Practice observing Jupiter and Saturn, so that you will be ready for
>>> Mars.
>>>
>
> That's the term I meant to use, "collimated". I had forgotten it
> because it's been a long while. I tried collimating it the cheap way.
> Taking one of those small black containers that hold a roll of film,
> making a small hole in the middle. Sticking a small dot in the middle
> of my mirror, and trying to align it with the screws. If that's not a
> good way to do it then I'll have to buy one of those laser
> collimators. But I'm also thinking about just getting one of the 8"
> dobs. Thanks for your suggestions.
|
| | | | |
Date: 03 May 2007 00:14:07
From: Chris L Peterson
Subject: Re: 4 inch reflector can't resolve Mars at all
|
On Thu, 03 May 2007 00:04:32 GMT, Bullseye <bulls@ei.com > wrote:
>That's the term I meant to use, "collimated". I had forgotten it
>because it's been a long while. I tried collimating it the cheap way.
>Taking one of those small black containers that hold a roll of film,
>making a small hole in the middle. Sticking a small dot in the middle
>of my mirror, and trying to align it with the screws. If that's not a
>good way to do it then I'll have to buy one of those laser
>collimators. But I'm also thinking about just getting one of the 8"
>dobs. Thanks for your suggestions.
Your collimation approach is error prone. And while laser collimators
generally work very well for Newtonians, they can also provide less than
perfect results, particularly when you are pushing magnification to its
limits, as is often the case with planetary viewing. For best results,
you should learn how to finish (or test) your collimation on a star.
_________________________________________________
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com
|
| |
Date: 02 May 2007 14:56:37
From: Starlord
Subject: Re: 4 inch reflector can't resolve Mars at all
|
Telescope Buyers FAQ
http://home.inreach.com/starlord
--
There are those who believe that life here, began out there, far across the
universe, with tribes of humans, who may have been the forefathers of the
Egyptians, or the Toltecs, or the Mayans. Some believe that they may yet be
brothers of man, who even now fight to survive, somewhere beyond the
heavens.
The Lone Sidewalk Astronomer of Rosamond
Telescope Buyers FAQ
http://home.inreach.com/starlord
Sidewalk Astronomy
www.sidewalkastronomy.info
The Church of Eternity
http://home.inreach.com/starlord/church/Eternity.html
AD World
http://www.adworld.netfirms.com/
"Bullseye" <bulls@ei.com > wrote in message
news:mcvh33592uhm1eo7c4uh1ib2ejnqkhfvib@4ax.com...
>I have a Nexstar 114GT and it can give visuals of the moon nicely
> (most scopes can I think) but I can't see sqwat when I point to Mars.
> I pointed to it 1-2 years ago when it was all over the news that it
> was close to Earth, but all I could see was a pink little ball, no
> features at all. Also in Saturn all I could see is a tiny little dot
> with a tiny circle around it. I've centered the scope and adjusted it
> all the ways I'm supposed to to get the best image (I've forgotten the
> exact terms that are used since I've ditched astronomy for awhile),
> but trust me I did. I just want to sell this sucker and get a new one.
> Can anyone recommend the best 4 inch reflectors out there for less
> than $500? Or maybe a very good 8 inch dob for less than $500?
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Date: 02 May 2007 16:03:55
From: Pat O'Connell
Subject: Re: 4 inch reflector can't resolve Mars at all
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Bullseye wrote:
> I have a Nexstar 114GT and it can give visuals of the moon nicely
> (most scopes can I think) but I can't see sqwat when I point to Mars.
> I pointed to it 1-2 years ago when it was all over the news that it
> was close to Earth, but all I could see was a pink little ball, no
> features at all.
I also have a 114GT, but it came from the factory fairly well
collimated. At the time you're talking about, I could see large patterns
of greenish gray and pink, and sometimes a polar cap, but nothing fine.
> Also in Saturn all I could see is a tiny little dot
> with a tiny circle around it.
You should be able to see more than that. Collimation for a 114GT
involves removing the correcting "Barlow" from the eyepiece holder,
doing a collimation, then replacing the Barlow.
> I've centered the scope and adjusted it
> all the ways I'm supposed to to get the best image (I've forgotten the
> exact terms that are used since I've ditched astronomy for awhile),
> but trust me I did. I just want to sell this sucker and get a new one.
> Can anyone recommend the best 4 inch reflectors out there for less
> than $500? Or maybe a very good 8 inch dob for less than $500?
Get a bigger scope than 4 inches to see more planetary details.
--
Pat O'Connell
[note munged EMail address]
Take nothing but pictures, Leave nothing but footprints,
Kill nothing but vandals...
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Date: 02 May 2007 17:55:23
From: Dennis Woos
Subject: Re: 4 inch reflector can't resolve Mars at all
|
"Bullseye" <bulls@ei.com > wrote in message
news:mcvh33592uhm1eo7c4uh1ib2ejnqkhfvib@4ax.com...
>I have a Nexstar 114GT and it can give visuals of the moon nicely
> (most scopes can I think) but I can't see sqwat when I point to Mars.
> I pointed to it 1-2 years ago when it was all over the news that it
> was close to Earth, but all I could see was a pink little ball, no
> features at all.
Look at: http://www.gmavt.net/~wooscon/MARS_0066_14_R_P.bmp
from 2-3 feet away. I think this is a pretty good idea of what Mars looked
like in a small (8" or less) scope with good optics during the last
opposition.
> Also in Saturn all I could see is a tiny little dot
> with a tiny circle around it.
Look at: http://www.gmavt.net/~wooscon/K3CCD_0017_250_R.gif
from 2-3 feet away. Saturn should look at least this good in a small (8" or
less) scope with good optics.
> I've centered the scope and adjusted it
> all the ways I'm supposed to to get the best image (I've forgotten the
> exact terms that are used since I've ditched astronomy for awhile),
> but trust me I did. I just want to sell this sucker and get a new one.
I would seek out your local astro club, and let the folks there check out
your scope. It may be that they can help you to get more satisfying
performance.
> Can anyone recommend the best 4 inch reflectors out there for less
> than $500? Or maybe a very good 8 inch dob for less than $500?
The Orion dobs get pretty good reviews. I don't think the movement is great
on any of the Chinese imports, but this can be fixed for not a whole lot of
time and money. Another option is to check out the StarGazer Steve kits,
which while a bit more expensive are by all reports great scopes, and you
will learn a lot by building it.
Dennis
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Date: 02 May 2007 14:54:58
From: laura halliday
Subject: Re: 4 inch reflector can't resolve Mars at all
|
On May 2, 9:21 pm, Bullseye <b...@ei.com > wrote:
> I have a Nexstar 114GT and it can give visuals of the moon nicely
> (most scopes can I think) but I can't see sqwat when I point to Mars.
> I pointed to it 1-2 years ago when it was all over the news that it
> was close to Earth, but all I could see was a pink little ball, no
> features at all. Also in Saturn all I could see is a tiny little dot
> with a tiny circle around it. I've centered the scope and adjusted it
> all the ways I'm supposed to to get the best image (I've forgotten the
> exact terms that are used since I've ditched astronomy for awhile),
> but trust me I did. I just want to sell this sucker and get a new one.
> Can anyone recommend the best 4 inch reflectors out there for less
> than $500? Or maybe a very good 8 inch dob for less than $500?
You've already got a pretty decent 4" reflector, and if it can't
resolve Saturn to your satisfaction, no other 4" reflector will be
able to.
With the usual proviso (planets are hard targets!), you might
want to have a look at what Synta/Orion/etc. have to offer in
the 8" Dob range.
You might also want to have a look through somebody
else's scope before spending more money.
Laura Halliday VE7LDH "Que les nuages soient notre
Grid: CN89mg pied a terre..."
ICBM: 49 16.05 N 122 56.92 W - Hospital/Shafte
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Date: 02 May 2007 15:00:17
From: Starlord
Subject: Re: 4 inch reflector can't resolve Mars at all
|
I have a Stargazer Steve 4.25inch F9 dob and then I built the F8 8inch dob I
named Babalon 8 and it was at the the last close pass of mars and I could
make out marks on MARS and it was awesome too.
The Lone Sidewalk Astronomer of Rosamond
Telescope Buyers FAQ
http://home.inreach.com/starlord
Sidewalk Astronomy
www.sidewalkastronomy.info
The Church of Eternity
http://home.inreach.com/starlord/church/Eternity.html
AD World
http://www.adworld.netfirms.com/
"laura halliday" <marsgal42@hotmail.com > wrote in message
news:1178142898.287360.80890@o5g2000hsb.googlegroups.com...
> On May 2, 9:21 pm, Bullseye <b...@ei.com> wrote:
>> I have a Nexstar 114GT and it can give visuals of the moon nicely
>> (most scopes can I think) but I can't see sqwat when I point to Mars.
>> I pointed to it 1-2 years ago when it was all over the news that it
>> was close to Earth, but all I could see was a pink little ball, no
>> features at all. Also in Saturn all I could see is a tiny little dot
>> with a tiny circle around it. I've centered the scope and adjusted it
>> all the ways I'm supposed to to get the best image (I've forgotten the
>> exact terms that are used since I've ditched astronomy for awhile),
>> but trust me I did. I just want to sell this sucker and get a new one.
>> Can anyone recommend the best 4 inch reflectors out there for less
>> than $500? Or maybe a very good 8 inch dob for less than $500?
>
> You've already got a pretty decent 4" reflector, and if it can't
> resolve Saturn to your satisfaction, no other 4" reflector will be
> able to.
>
> With the usual proviso (planets are hard targets!), you might
> want to have a look at what Synta/Orion/etc. have to offer in
> the 8" Dob range.
>
> You might also want to have a look through somebody
> else's scope before spending more money.
>
> Laura Halliday VE7LDH "Que les nuages soient notre
> Grid: CN89mg pied a terre..."
> ICBM: 49 16.05 N 122 56.92 W - Hospital/Shafte
>
|
| | | |
Date: 02 May 2007 19:50:20
From: Borked Pseudo Mailed
Subject: Re: Shitetards 4 inch arsehole can't take the star parties any more
|
the spammertard of rosatard <starlord@sidewalkastronomy.info > spammed:
>I have a 4.25inch shite hole big enuogh for my nancy buggers 8inch chubby ramrod
>i numed his chubby babelshite 8 and it was at the the last close pass up my arsehole
>since this morning and I cuold make out with mark up my sphincter where his chubby
> riped the scabs off he festering pustules on my arsehole and it was fawking
>awsume felching gerbils too but my arsehole is so fawking sore now i have to
> stop leting the star party buggers pull trains on my arsehole
>
> i spam every fawking five minutes again i am a spammer and stalker and spammer
>spam spam spam fawking spam stalk spam i am dennis bishop i am shitetard
>i have a 70 iq i am a barmy fawking dishonourably discharged drunken bum i am
>one dumb fawking arsehole i was born in a fawking shite hole in cincinnati ohio on
>december 10 1948 to a fawking nappy headed whore i am mulatto
>
> i am the spelling bee champion of rosatard where arsetronomers whip out their chubby
>telescopes and investigate uranus at the star parties at night in the dark
>in front of children fawk ooh aah
>
fawk shitetard youre from the slums of cincinnatti fawking ohio what a
fawking ghetto shite hole your heroin addict mum must have dropped you on your noggin
a lot when you were a baby no wonder youre such a fawking barmy retard
a mongoloid down syndrome shitetard you really are the dumbest fawking
arsehole west of the pond how do you tie your shoelaces must have your nancy
landlord do it for you in exchange for buggering your shitey arsehole does he
give you a reach around we know what you do to get bugger discounts on your rent
for a good time call 661 256 2175
and visit dennis bishop at his famous felching gerbil farm at
470 20th st w rosamond ca post code 93560
trailer trash lot number 23
denise blipshite the self pity thirty percent cripple bum hobbling along with his ickle
toy red wagon in tow it goes squeak squeak all the way up to the local
fawking off license from 20th st and back
squeak squeak squeak squeak hobble hobble glug glug brrrraaaaaapppppp
20th st must be fawking littered with empty pint bottles lager and ale every
fawking brand the off license carries
give us your daily fawking antelope valley weather centre report shitetard
because we care
shitetard we can see that you stuck your spammy gobshite rubbish siggy lines back in
your fawking gobshite spamming and stalking in saa and aa
you must need more self pity cripple donations to your lager fund since you wrecked
your hand me down hunk of fawking shite van last week fawk two drunk driving wrecks in
as many months what was that hunk of shite you wrecked in february a 1974 rusted out
fawking piece of shite trying to set the antelope valley record for driving hard
pissed arseholed and wrecking your fawking piece of shite jalopies on the unsafe streets
of rosamond california fawking drunk drivers fawking shitetard
spam spam stalk stalk spam stalk spam stalk gobshite rubbish all fawking day
long
spam abuse complaints to
abuse@inreach.com
starlord@sidewalkastronomy.info
news.admin.net-abuse.usenet
news.admin.net-abuse.sightings
administrator@cafepress.com
http://www.publicdomainregistry.com/contactus/report-spam/
>
>
>
>
>"laura halliday" <marsgal42@hotmail.com> wrote in message
>news:1178142898.287360.80890@o5g2000hsb.googlegroups.com...
>> On May 2, 9:21 pm, Bullseye <b...@ei.com> wrote:
>>> I have a Nexstar 114GT and it can give visuals of the moon nicely
>>> (most scopes can I think) but I can't see sqwat when I point to Mars.
>>> I pointed to it 1-2 years ago when it was all over the news that it
>>> was close to Earth, but all I could see was a pink little ball, no
>>> features at all. Also in Saturn all I could see is a tiny little dot
>>> with a tiny circle around it. I've centered the scope and adjusted it
>>> all the ways I'm supposed to to get the best image (I've forgotten the
>>> exact terms that are used since I've ditched astronomy for awhile),
>>> but trust me I did. I just want to sell this sucker and get a new one.
>>> Can anyone recommend the best 4 inch reflectors out there for less
>>> than $500? Or maybe a very good 8 inch dob for less than $500?
>>
>> You've already got a pretty decent 4" reflector, and if it can't
>> resolve Saturn to your satisfaction, no other 4" reflector will be
>> able to.
>>
>> With the usual proviso (planets are hard targets!), you might
>> want to have a look at what Synta/Orion/etc. have to offer in
>> the 8" Dob range.
>>
>> You might also want to have a look through somebody
>> else's scope before spending more money.
>>
>> Laura Halliday VE7LDH "Que les nuages soient notre
>> Grid: CN89mg pied a terre..."
>> ICBM: 49 16.05 N 122 56.92 W - Hospital/Shafte
>>
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Date: 02 May 2007 21:44:52
From: Chris L Peterson
Subject: Re: 4 inch reflector can't resolve Mars at all
|
On Wed, 02 May 2007 21:21:44 GMT, Bullseye <bulls@ei.com > wrote:
>I have a Nexstar 114GT and it can give visuals of the moon nicely
>(most scopes can I think) but I can't see sqwat when I point to Mars.
>I pointed to it 1-2 years ago when it was all over the news that it
>was close to Earth, but all I could see was a pink little ball, no
>features at all. Also in Saturn all I could see is a tiny little dot
>with a tiny circle around it. I've centered the scope and adjusted it
>all the ways I'm supposed to to get the best image (I've forgotten the
>exact terms that are used since I've ditched astronomy for awhile),
>but trust me I did. I just want to sell this sucker and get a new one.
>Can anyone recommend the best 4 inch reflectors out there for less
>than $500? Or maybe a very good 8 inch dob for less than $500?
Odds are that your scope is just fine, and replacing it with another of
the same aperture won't make a difference. It's very likely that you
need to collimate it better. It also sounds as if you might be using it
at too low a magnification (although a higher magnification will
certainly require good collimation).
An 8" scope (try Orion's offerings) will significantly outperform your
4" scope, but the requirement for good collimation remains.
_________________________________________________
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com
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Date: 02 May 2007 22:14:39
From: Chris L Peterson
Subject: Re: 4 inch reflector can't resolve Mars at all
|
On Wed, 02 May 2007 21:44:52 GMT, Chris L Peterson
<clp@alumni.caltech.edu > wrote:
>An 8" scope (try Orion's offerings) will significantly outperform your
>4" scope, but the requirement for good collimation remains.
I'll also add that you shouldn't overlook the value of tracking in your
current scope. I'm usually frustrated using a Dob for high power
observing of the Moon and planets, because the object drifts so quickly
out of the field. It can be hard just to simply observe.
_________________________________________________
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com
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Date: 02 May 2007 20:30:55
From: Phoon Hencman
Subject: Re: 4 inch reflector can't resolve Mars at all
|
On 2007-05-02 18:14:39 -0400, Chris L Peterson <clp@alumni.caltech.edu > said:
> On Wed, 02 May 2007 21:44:52 GMT, Chris L Peterson
> <clp@alumni.caltech.edu> wrote:
>
>> An 8" scope (try Orion's offerings) will significantly outperform your
>> 4" scope, but the requirement for good collimation remains.
>
> I'll also add that you shouldn't overlook the value of tracking in your
> current scope. I'm usually frustrated using a Dob for high power
> observing of the Moon and planets, because the object drifts so quickly
> out of the field. It can be hard just to simply observe.
>
> _
And remember, seeing conditions play an IMPORtANT part too.
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