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Main
Date: 15 Sep 2007 23:01:09
From: Terry A Haimann
Subject: eye pieces
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I own a 20cm sct (LX-90.) Based on that info, what eye pieces would
maxamize my investement w/o breaking the bank. If I buy them seperatly,
I could possibly afford $200 an e.p. I have been using Meade Series 4000
Super Plossls. I have a 32, 15 and a 6.4mm e.p. The 32 and 15 get the most
use.
Thx, Terry
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Date: 17 Sep 2007 11:23:40
From:
Subject: Re: eye pieces
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Terry A Haimann wrote:
> I think they have more reflections then they should and if you put
> them up to a bright light I can see black specks in the glass. I
> suspect that can't be good for light transmission. But I suspect
> they do ok on dso's. I am just wondering if there is a better choice
> in my price range.
Most eyepieces don't look very good when held up to a bright light,
any more than most objectives do. When you do that, you are not
comparing apples to apples. You are seeing the scattering of the
bright light by dust or occlusions on the surfaces, but you're seeing
that against a backdrop that lacks the bright light itself (unless
you're looking through the eyepiece at the bright light). Most optics
will look bad under those circumstances.
Plossls are fine, if you can find them in the range you want, but you
might run into an eye relief issue with them--Plossls do not have a
ton of eye relief. The 10 mm Radian is generally well-regarded, has
comfortable eye-relief, a reasonably wide field of view (60 degrees),
and is basically orthoscopic (distortion-free).
If you can handle shorter eye relief and can find one of these, you
might consider one of the University Optics orthoscopics. I have a
9 mm that I like quite a bit, although I don't use it much anymore.
Inexpensive, with a modest field of view (45 degrees), and as the
name suggests, orthoscopic. Eye relief probably precludes wearing
glasses.
--
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
use it very m
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Date: 16 Sep 2007 18:10:07
From: Quadibloc
Subject: Re: eye pieces
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Terry A Haimann wrote:
> I own a 20cm sct (LX-90.) Based on that info, what eye pieces would
> maxamize my investement w/o breaking the bank. If I buy them seperatly,
> I could possibly afford $200 an e.p. I have been using Meade Series 4000
> Super Plossls. I have a 32, 15 and a 6.4mm e.p. The 32 and 15 get the most
> use.
200mm aperture, or what people used to call 8 inches. These usually
have a focal ratio of f/10.
60x per inch, maximum usable magnification 480x, 80-inch focal length.
So your highest-power eyepiece should have a focal length of 4mm.
7x50 binoculars are night glasses, so that would be 28x200 for an
equivalent exit pupil. For richest-field use, if you could somehow
attach an eyepiece with a 70mm focal length to the telescope, that
would serve there.
Given that the 32mm and 15mm eyepieces are the ones that get the most
use, I suppose I would be inclined to recommend perhaps an eyepiece
just like one I bought recently - and quite inexpensively.
I bought an eyepiece with a 70 degree apparent field, and 19mm focal
length, and I found that quite impressive; such an eyepiece is normal-
sized, not big and heavy like some Naglers and their competition, but
the field is just about as wide as one might want.
You should be able to get one like that for under $50.
I own, as one of my earlier eyepiece purchases, a 40mm Kellner
eyepiece with a 1 1/4" barrel, so if you can find one, that might be
good to have for completeness. (Anything fancier in a 40mm would need
a 2" barrel, but if your scope has one, do try for that or a lower
magnification as an option.) The only other thing you seem to need to
have to round out your eyepiece set would be something with a focal
length from 9 to 12mm, to have a higher magnification not quite so
high as that of a 6.4mm eyepiece.
John Savard
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Date: 17 Sep 2007 17:26:45
From: Margo Schulter
Subject: Re: eye pieces
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Quadibloc <jsavard@ecn.ab.ca > wrote:
> Terry A Haimann wrote:
>> I own a 20cm sct (LX-90.) Based on that info, what eye pieces would
>> maxamize my investement w/o breaking the bank. If I buy them seperatly,
>> I could possibly afford $200 an e.p. I have been using Meade Series 4000
>> Super Plossls. I have a 32, 15 and a 6.4mm e.p. The 32 and 15 get the most
>> use.
>
> 200mm aperture, or what people used to call 8 inches. These usually
> have a focal ratio of f/10.
>
Hi, there, Quadibloc and all.
Please let me quickly point out, as an aside, that while the decision
of whether to use oldstyle English units (inches, feet) or metrical
units is often one of style, actually 8 inches equals 203.2mm.
Thus 200mm, about 7.9 inches, is a very slightly smaller aperture.
The differences, of course, are small enough that it's often convenient
to ignore them, and call a true 8" scope "200mm," or a true 200mm scope
"8 inches."
Thus with my 200mm/1200mm Sky-Watcher Dob, we have a focal ratio of f/6,
and a 7.5mm eyepiece should yield 160X. With a 203mm/1200mm scope,
another common specification, the focal length is the same, but at a
slightly faster f/5.91. With 203mm/1219mm, 8 inches at f/6, the focal
length is a tad longer, so that a 7.5mm eyepiece yields around 162.5X.
Again, these are rather minute distinctions.
Most appreciatively,
Margo Schulter
mschulter@calweb.com
Lat. 38.566 Long. -121.430
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Date: 17 Sep 2007 17:12:33
From: Steve Paul
Subject: Re: eye pieces
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"Margo Schulter" wrote:
> Thus with my 200mm/1200mm Sky-Watcher Dob, we have a focal ratio of f/6,
> and a 7.5mm eyepiece should yield 160X. With a 203mm/1200mm scope,
> another common specification, the focal length is the same, but at a
> slightly faster f/5.91. With 203mm/1219mm, 8 inches at f/6, the focal
> length is a tad longer, so that a 7.5mm eyepiece yields around 162.5X.
>
> Again, these are rather minute distinctions.
The Meade Starfinder is designated as a 12.5" F5 but the mirror on mine was
marked on the backside in hand written permanent marker as FL 59.7", F4.77.
A 7.5mm Plossl may be longer or shorter, or have a wider or smaller field
stop than the design and numbers on the barrel suggest.
-Steve P.
--
Posted via a free Usenet account from http://www.teranews.com
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Date: 18 Sep 2007 21:49:48
From: David Knisely
Subject: Re: eye pieces
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Steve Paul wrote:
> The Meade Starfinder is designated as a 12.5" F5 but the mirror on mine was
> marked on the backside in hand written permanent marker as FL 59.7", F4.77.
Actually, the 12.5 inch Meade Starfinders are specified by the
manufacturer to be f/4.8 (60 inch "nominal" focal length) and not f/5.
59.7 inches is well within standard manufacturer tolerance for telescope
mirrors (only 0.5 percent low), as most generally have less than two
percent variance from their stated specification. 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 *
**********************************************
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Date: 17 Sep 2007 16:00:16
From: Jan Owen
Subject: Re: eye pieces
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"Steve Paul" <smarshallpaul@gmail.com > wrote in message
news:46eee1bc$0$16321$88260bb3@free.teranews.com...
>
> "Margo Schulter" wrote:
>
>> Thus with my 200mm/1200mm Sky-Watcher Dob, we have a focal ratio of f/6,
>> and a 7.5mm eyepiece should yield 160X. With a 203mm/1200mm scope,
>> another common specification, the focal length is the same, but at a
>> slightly faster f/5.91. With 203mm/1219mm, 8 inches at f/6, the focal
>> length is a tad longer, so that a 7.5mm eyepiece yields around 162.5X.
>>
>> Again, these are rather minute distinctions.
>
> The Meade Starfinder is designated as a 12.5" F5 but the mirror on mine
> was marked on the backside in hand written permanent marker as FL 59.7",
> F4.77.
>
> A 7.5mm Plossl may be longer or shorter, or have a wider or smaller field
> stop than the design and numbers on the barrel suggest.
>
> -Steve P.
>
This is virtually always the case, with varying degrees of variation, scope
to scope & manufacturer to manufacturer...
Because a telescope's specification sheet says it's f/6, or whatever,
doesn't mean it's exactly f/6... It'll be however close it came to that
when the optical department, or final finisher was done with it, and may be
f/5.95, or f/6.07, or whatever... Some manufacturers will TELL you the
approximate range of variation, but others don't... And if THAT's not
enough, the mirror on any given reflector will virtually always have a bevel
at the edge of it's surface... And the bevel may be nearly 1/8" wide,
varying from mirror to mirror, and from reason to reason. This is done to
cover up a slightly turned edge, or to eliminate one or more small chips at
the edge, but whichever the case, unless the mirror blank was oversize in
the FIRST place, it makes the REAL aperture smaller, and when you combine
that with the fact that the focal length wasn't what you thought, EITHER,
going by the manufacturer's spec sheet isn't all that precise...
In fact, I noted that Margo mentioned that her scope was 200mm... Yet when
I went to her scope manufacturer's website, THEY list it's aperture at
203mm. Then it says the focal length is 1200, which, of all the ones
they've made, only a relatively few are EXACTLY 1200mm in focal length...
So, we shouldn't really spend a lot of time using the manufacturer's
specification sheets to draw multi-decimal-place conclusions using them...
As in YOUR experience (and mine), many mirrors have the REAL focal length
marked on the back or edge, either etched in the glass, or with some sort of
permanent marker... If not, it's not THAT difficult to measure the REAL
focal length, but many folks don't, can't, or don't want to be bothered...
And unless you're doing something critical, it's really not THAT
important... No, you WON'T be observing at the 205X you thought you were;
you may be observing at 209X, or 199X. But does this REALLY matter??? It
MAY, but if it doesn't, who CARES???
--
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
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Date: 18 Sep 2007 00:08:59
From: Margo Schulter
Subject: Re: eye pieces
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Jan Owen <janowen1@cox.net > wrote:
> In fact, I noted that Margo mentioned that her scope was 200mm... Yet when
> I went to her scope manufacturer's website, THEY list it's aperture at
> 203mm. Then it says the focal length is 1200, which, of all the ones
> they've made, only a relatively few are EXACTLY 1200mm in focal length...
> So, we shouldn't really spend a lot of time using the manufacturer's
> specification sheets to draw multi-decimal-place conclusions using them...
Hi, Jan and Steve and all.
First, please let me agree with you and Steve that in practice,
the tolerances or variations that attach to a spec like "200mm f/6"
might be greater than the theoretical distinction between that and
"203mm f/5.91," for example.
Just to clarify the situation about the stated specs for my scope.
On the Web, I've also seen 203mm/1200mm; but the printed information
on the OTA and also the manual say 200mm/1200mm. Given the inevitable
variations in practice, maybe inconsistent specs for this scope
actually could be considered a representation of some of the likely
variations <grin >.
Jan and Steve, your cautions about doing calculations to an unrealistic
number of significant digits are, of course, right on point! Maybe the
main reason I tend to like using the 200mm/1200mm figures is that this
often leads to nice round numbers for magnification or exit pupil or
the like <grin >.
Most appreciatively,
Margo Schulter
mschulter@calweb.com
Lat. 38.566 Long. -121.430
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Date: 16 Sep 2007 10:02:17
From:
Subject: Re: eye pieces
|
On Sep 15, 5:01 pm, Terry A Haimann <te...@Pegasus.oldboy > wrote:
> I own a 20cm sct (LX-90.) Based on that info, what eye pieces would
> maxamize my investement w/o breaking the bank. If I buy them seperatly,
> I could possibly afford $200 an e.p. I have been using Meade Series 4000
> Super Plossls. I have a 32, 15 and a 6.4mm e.p.
Hi Terry,
I'm not familiar with the Meade Super Plossls (I live a rather
isolated existance out in the middle of nowhere ;-)
I've been satisfied with the $55 or three for $145 (plus shipping)
Orion HighLight Plossls. I have all the HL Plossls from the 26mm
(25mm now) through the 7.5mm and have used them with f/5 and f/6
telescopes from 80mm to 300mm aperture. I would suggest the same set
(with the possible exception of the 7.5mm depending upon the
"sharpness" of your scope's optics). You could pay more for a Plossl;
but I doubt that you would notice any improvement in performance.
For the maximum true field of view (with a 1.25" eyepiece) I use a
35mm Ultima. Other eyepieces are available that would fill the same
niche. Circumstances of convenience resulted in my choosing the
Ultima. An eyepiece such as this might permit you to set aside your
focal reducer -- at least for visual use. By the way, in comparison
to the 35mm Ultima (or similar eyepiece) a 40mm eyepiece (with a 1.25"
barrel) would be a poorer choice resulting in reduced magnification
(and contrast) and smaller apparent field with no increase in true
field size.
Eyepieces with wider apparent fields (than the Plossls) are nice to
have; but they tend to get pretty expensive -- especially if you
expect them the maintain image sharpness to the edge of the field.
For *most* objects the wider fields are not needed. Thus there's no
need for the additional lens elements and/or additional air-glass
surfaces. That being said, I *do* have some wide-field eyepieces that
I treasure and use from time to time . . .
Bill Greer
To sketch is to see.
http://cejour.blogspot.com
http://www.rangeweb.net/~sketcher
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Date: 16 Sep 2007 10:42:05
From: Steve Paul
Subject: Re: eye pieces
|
"Terry A Haimann" <terry@Pegasus.oldboy > wrote in message
news:pan.2007.09.15.23.00.19.830239@Pegasus.oldboy...
>I own a 20cm sct (LX-90.) Based on that info, what eye pieces would
> maxamize my investement w/o breaking the bank. If I buy them seperatly,
> I could possibly afford $200 an e.p. I have been using Meade Series 4000
> Super Plossls. I have a 32, 15 and a 6.4mm e.p. The 32 and 15 get the most
> use.
>
> Thx, Terry
The widest field of view in an 8" SCT is pretty much achievable with a 32mm
Plossl and an F6.3 Focal Reducer/Corrector. You _can_ use a 2" eyepiece with
a greater field stop than the 32mm Plossl, but the R/C isn't as expensive
and will work with all your eyepieces... just a thought.
You can also go to all the expense of well corrected 65+ wide field and 80+
ultra wide field eyepieces to increase the field of view at same powers (the
only real benefit of using them in an SCT, IMO).
That is, a 13mm Nagler T6 at 80 degree AFOV, gives a bit larger field of
view at 153x as the 50 degree AFOV 18mm Ultima does at 111x. (If you think
you need 153x at a half degree of true field.)
My most used eyepiece in my old C8 was the 18mm Ultima for DSO's and used in
conjunction with an Ultima Barlow (2x) for planets.
110x and 220x (we generally have a 240x seeing limit in these parts on a
_good_ night)
Eventually sold the scope, but kept the Ultima eyepieces and barlow. I also
have a 12.5mm Ultima, and a 30mm Ultima. The 30 shows more defects out at
the edge than the other two in fast scopes, but I still use it in scopes
down to F5 as a wide field eyepiece. It works just fine in the F6 AstroTech
66ED, but it is a bit harsh in the F5 6" reflector (not at all unusable
though, and some of that is my astigmatism with a 6mm exit pupil).
The Orion Ultrascopics are reportedly the same eyepiece design as the
Ultima, but I believe they come in nickel values (10mm, 15mm, 25mm, etc.)...
not that there's a thing wrong with that.
My $.02,
Steve P.
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Date: 16 Sep 2007 14:54:13
From: Terry A Haimann
Subject: Re: eye pieces
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I should mention that I do own a 6.3 focal reducer and it was great for
searching for Messier objects. but with the Herschel 400 I need higher
magnification, also there is some loss of light when using the fr.
On Sun, 16 Sep 2007 10:42:05 -0400, Steve Paul wrote:
>
> "Terry A Haimann" <terry@Pegasus.oldboy> wrote in message
> news:pan.2007.09.15.23.00.19.830239@Pegasus.oldboy...
>>I own a 20cm sct (LX-90.) Based on that info, what eye pieces would
>> maxamize my investement w/o breaking the bank. If I buy them seperatly,
>> I could possibly afford $200 an e.p. I have been using Meade Series 4000
>> Super Plossls. I have a 32, 15 and a 6.4mm e.p. The 32 and 15 get the most
>> use.
>>
>> Thx, Terry
>
>
> The widest field of view in an 8" SCT is pretty much achievable with a 32mm
> Plossl and an F6.3 Focal Reducer/Corrector. You _can_ use a 2" eyepiece with
> a greater field stop than the 32mm Plossl, but the R/C isn't as expensive
> and will work with all your eyepieces... just a thought.
>
> You can also go to all the expense of well corrected 65+ wide field and 80+
> ultra wide field eyepieces to increase the field of view at same powers (the
> only real benefit of using them in an SCT, IMO).
>
> That is, a 13mm Nagler T6 at 80 degree AFOV, gives a bit larger field of
> view at 153x as the 50 degree AFOV 18mm Ultima does at 111x. (If you think
> you need 153x at a half degree of true field.)
>
> My most used eyepiece in my old C8 was the 18mm Ultima for DSO's and used in
> conjunction with an Ultima Barlow (2x) for planets.
>
> 110x and 220x (we generally have a 240x seeing limit in these parts on a
> _good_ night)
>
> Eventually sold the scope, but kept the Ultima eyepieces and barlow. I also
> have a 12.5mm Ultima, and a 30mm Ultima. The 30 shows more defects out at
> the edge than the other two in fast scopes, but I still use it in scopes
> down to F5 as a wide field eyepiece. It works just fine in the F6 AstroTech
> 66ED, but it is a bit harsh in the F5 6" reflector (not at all unusable
> though, and some of that is my astigmatism with a 6mm exit pupil).
>
> The Orion Ultrascopics are reportedly the same eyepiece design as the
> Ultima, but I believe they come in nickel values (10mm, 15mm, 25mm, etc.)...
> not that there's a thing wrong with that.
>
> My $.02,
> Steve P.
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Date: 15 Sep 2007 19:45:14
From: Dennis Woos
Subject: Re: eye pieces
|
"Terry A Haimann" <terry@Pegasus.oldboy > wrote in message
news:pan.2007.09.15.23.00.19.830239@Pegasus.oldboy...
>I own a 20cm sct (LX-90.) Based on that info, what eye pieces would
> maxamize my investement w/o breaking the bank. If I buy them seperatly,
> I could possibly afford $200 an e.p. I have been using Meade Series 4000
> Super Plossls. I have a 32, 15 and a 6.4mm e.p. The 32 and 15 get the most
> use.
>
> Thx, Terry
In what ways are you unhappy with the eyepieces that you already have?
Dennis
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Date: 16 Sep 2007 00:46:05
From: Terry A Haimann
Subject: Re: eye pieces
|
I think they have more reflections then they should and if you put them up
to a bright light I can see black specks in the glass. I suspect that
can't be good for light transmission. But I suspect they do ok on dso's.
I am just wondering if there is a better choice in my price range.
On Sat, 15 Sep 2007 19:45:14 -0400, Dennis Woos wrote:
>
> "Terry A Haimann" <terry@Pegasus.oldboy> wrote in message
> news:pan.2007.09.15.23.00.19.830239@Pegasus.oldboy...
>>I own a 20cm sct (LX-90.) Based on that info, what eye pieces would
>> maxamize my investement w/o breaking the bank. If I buy them seperatly,
>> I could possibly afford $200 an e.p. I have been using Meade Series 4000
>> Super Plossls. I have a 32, 15 and a 6.4mm e.p. The 32 and 15 get the most
>> use.
>>
>> Thx, Terry
>
> In what ways are you unhappy with the eyepieces that you already have?
>
> Dennis
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Date: 15 Sep 2007 22:14:12
From: Dennis Woos
Subject: Re: eye pieces
|
>I think they have more reflections then they should and if you put them up
> to a bright light I can see black specks in the glass. I suspect that
> can't be good for light transmission. But I suspect they do ok on dso's.
> I am just wondering if there is a better choice in my price range.
>
I think that a lot of folks buy high-end eyepieces thinking that they will
provide greatly improved views, and they won't. Decent quaility Plossls
(like those you have) should perform nearly as well as any expensive
eyepiece. What Plossls don't have is very wide fields and, in shorter focal
lengths, great eye relief. The best thing you can do is attend some
observing events held by your local astro club and try some better/more
expensive eyepieces, and judge their merits for yourself. However, I do
agree with Howard that an eyepiece that provides 200-220x (10-9mm) would be
a very useful addition, and this is a chance to try a different mfg/design.
Some possibilities to look at are BO/TMB Planetary 9mm, Baader Hyperions,
Televue Plossls and Radians. Of course, there are others. If it was me, I
would get the BO/TMB 9mm, but the Televue Plossls have never disappointed me
either. If you aren't crazy about the views with the new (and better?)
eyepiece, then I would suspect the scope optics (assuming that the ota is
collimated, cooled down, the seeing is good, etc.) Compare the views you are
getting to those through the other scopes at observing events.
Dennis
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Date: 15 Sep 2007 19:48:05
From: Howard Lester
Subject: Re: eye pieces
|
"Dennis Woos" wrote
> agree with Howard that an eyepiece that provides 200-220x (10-9mm) would
> be a very useful addition, and this is a chance to try a different
> mfg/design. Some possibilities to look at are BO/TMB Planetary 9mm, Baader
> Hyperions, Televue Plossls and Radians. Of course, there are others. If it
> was me, I would get the BO/TMB 9mm, but the Televue Plossls have never
> disappointed me either.
Dennis, I love my TeleVue 8mm Plossl and would highly recommend the line,
but they make only 8's and 11's.... not 9 or 10's, the latter range being
what I thought would suit Terry best. The Burgess/TMB 9 might be a good
choice, yes, especially with its apparent field of 60 degrees.
Also, can a focal length longer than 32mm be well suited for his SCT? He
might benefit from some widefield 40mm eyepiece. ?
Howard
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Date: 16 Sep 2007 08:30:48
From: Dennis Woos
Subject: Re: eye pieces
|
> Dennis, I love my TeleVue 8mm Plossl and would highly recommend the line,
> but they make only 8's and 11's.... not 9 or 10's, the latter range being
> what I thought would suit Terry best. The Burgess/TMB 9 might be a good
> choice, yes, especially with its apparent field of 60 degrees.
>
> Also, can a focal length longer than 32mm be well suited for his SCT? He
> might benefit from some widefield 40mm eyepiece. ?
If he has a 2" visual back/diagonal then a low-power/wide-field eyepiece
would be another great addition. Fortunately, there are more and more
choices in this area. I traded a 30mm 1rpd to a guy in our club with an 8"
LX200, and he loves it for this purpose. There are also many better/more
expensive options, like the new(ish) TMB Paragon 40mm and 30mm, which get
great reviews and go for around $250.
Dennis
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Date: 15 Sep 2007 16:44:25
From: Howard Lester
Subject: Re: eye pieces
|
"Terry A Haimann" wrote
> I could possibly afford $200 an e.p. I have been using Meade Series 4000
> Super Plossls. I have a 32, 15 and a 6.4mm e.p. The 32 and 15 get the most
> use.
What I see you lacking is something in the 9-10mm range. This $89 9mm Series
5000 Meade will give you 225x, which is a good practical lunar and planetary
limit on most nights for your 8" SCT. Disregard the review on this site.
He's using an f/4.5 reflector and complains about the lack of edge
sharpness.... *sigh* as well as color issues in an achromat refractor.
http://www.buytelescopes.com/product.asp?t=26&pid=8184&m=
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