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Main
Date: 25 Jun 2007 20:30:36
From: mitch
Subject: I'm Sold !
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http://www.cloudynights.com/item.php?item_id=86
just ordered one. $230 CAD total
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Date: 28 Jun 2007 09:18:24
From: ULB
Subject: Re: I'm Sold !
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On Jun 26, 7:07 pm, "mitch" <m...@nospam.net > wrote:
> Personally, I've
>
> > used it and am unable to see any difference in optical quality between
> > it and an Orion 2" Shorty barlow. But maybe with your eyes, or your
> > eyepieces, you will (it's no secret that I'm not primarily a visual
> > astronomer, after all <g>).
>
> Ok...but what about 1.25 inchers? Your comparison isn't sound. The
> 2" 4 X powermate is about 100 bucks more and I bet it would
> blow your Orion out of the water.
I have the 5x powermate. Not certain if they make it anymore. I used
it for imaging planets a few years back with my SCT. It worked well,
almost too much power.
I also used it observe mars a few years back when Mars was supposedly
its closest in x years. From memory it was quite a sight.
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Date: 29 Jun 2007 10:55:19
From: Michael McCulloch
Subject: Re: I'm Sold !
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On Thu, 28 Jun 2007 09:18:24 -0700, ULB
<ultralightbackpacker@yahoo.com > wrote:
>I have the 5x powermate. Not certain if they make it anymore. I used
>it for imaging planets a few years back with my SCT. It worked well,
>almost too much power.
>
>I also used it observe mars a few years back when Mars was supposedly
>its closest in x years. From memory it was quite a sight.
I use a 5x Powermate with my 105mm apo and my longer focal length
Pentax EPs. It is superb for splitting close double stars on steady
nights. The star image is textbook.
---
Michael McCulloch
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Date: 26 Jun 2007 17:41:10
From: Rich
Subject: Re: I'm Sold !
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On Jun 26, 2:47 pm, "mitch" <m...@nospam.net > wrote:
> Well, the whole point of the cloudy nights article makes the powermate clear
> over
> standard barlows.
Exactly. Something you can't chalk up to only having (maybe) better
coatings and perhaps better surface polish.
Of course we don't know if any of that is true, since mfgs never
disclose this kind of info for eyepieces and the like.
-Rich
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Date: 26 Jun 2007 17:39:08
From: Rich
Subject: Re: I'm Sold !
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On Jun 26, 1:33 pm, LarryG <larryg...@yahoo.com > wrote:
> On Jun 26, 11:51 am, Rich <rander3...@gmail.com> wrote:
>
> > On Jun 25, 4:30 pm, "mitch" <m...@nospam.net> wrote:
>
> > >http://www.cloudynights.com/item.php?item_id=86
>
> > > just ordered one. $230 CAD total
>
> > I can't help thinking that for $230, I could order a negative achromat
> > with "certified" wavefront accuracy from any good optical supply
> > house.
> > With eyepieces, barlows, etc, from telescope companies, we have no
> > way of knowing what their true specs are. I've often wondered why we
> > often ask for this with the telescopes, but never the optical
> > accessories.
>
> Perhaps because the wave-rating of eyepieces is simply much less
> important.
So and eyepiece whose whole eyelens is being used by the light cone
can be optical junk and still work well?
I don't think so. This is the kind of reasoning a certain mfg. used
when trying to sell expensive 2" diagonal mirrors with shapes like
potato chips, convenient for the mfg, not so for the user.
>
> If we were to expect quarter-wave optical perfection all the way
> through the system, the manufacturing costs of even a fairly simple
> Plossl eyepiece would be "astronomical", approaching the cost of a
> modest size telescope. Eight optical surfaces would have to be
> individually corrected, and then appropriately matched to meet
> a needlessly stringent requirement.
>
True, and one more good reason why a simple, two achromat eyepiece
often tends to be
much better on planets.
> And then, the observer's own vision system (eye, glasses / contacts)
> would have to be corrected to quarter wave.
Then why not settle for a 1 wave telescope? Think how cheap it would
be!
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Date: 26 Jun 2007 10:48:27
From: benk
Subject: Re: I'm Sold !
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On Jun 26, 1:33 pm, LarryG <larryg...@yahoo.com > wrote:
> On Jun 26, 11:51 am, Rich <rander3...@gmail.com> wrote:
>
> > On Jun 25, 4:30 pm, "mitch" <m...@nospam.net> wrote:
>
> > >http://www.cloudynights.com/item.php?item_id=86
>
> > > just ordered one. $230 CAD total
>
> > I can't help thinking that for $230, I could order a negative achromat
> > with "certified" wavefront accuracy from any good optical supply
> > house.
> > With eyepieces, barlows, etc, from telescope companies, we have no
> > way of knowing what their true specs are. I've often wondered why we
> > often ask for this with the telescopes, but never the optical
> > accessories.
>
> Perhaps because the wave-rating of eyepieces is simply much less
> important.
>
> If we were to expect quarter-wave optical perfection all the way
> through the system, the manufacturing costs of even a fairly simple
> Plossl eyepiece would be "astronomical", approaching the cost of a
> modest size telescope. Eight optical surfaces would have to be
> individually corrected, and then appropriately matched to meet
> a needlessly stringent requirement.
>
> And then, the observer's own vision system (eye, glasses / contacts)
> would have to be corrected to quarter wave. At the moment, I am
> not aware of any corrective surgery which can even hope to guarantee
> any wave-front final accuracy even close to one-wave, let alone one-
> quarter wave.
>
> Of course, if you're Rich-enough, I'm sure you can afford it! ;-)
>
> Cheers,
> Larry G.
Good point. Does that mean, then, that eyepiece/barlow aberrations are
less critical than objective lens/mirror aberrations? If so, why? Just
the much much smaller surface area?
Sounds plausible to me, but I don't know how to error-check my wild
guesses. Can anyone help?
--Ben
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Date: 26 Jun 2007 18:02:38
From: Chris L Peterson
Subject: Re: I'm Sold !
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On Tue, 26 Jun 2007 10:48:27 -0700, benk <ben@kolstad.com > wrote:
>Good point. Does that mean, then, that eyepiece/barlow aberrations are
>less critical than objective lens/mirror aberrations? If so, why? Just
>the much much smaller surface area?
Consider what most optical aberrations are at a small scale: a ray which
should leave a surface at some angle A actually leaves at an angle A+dA.
That's the case whether you are talking about some huge objective or an
internal surface in an EP. The value of dA doesn't scale with the size
of the optic. The effect of that deviated ray, however, increases as you
get farther from the aberrating surface. Even a small angular aberration
at the objective can become a large linear aberration at the focal
plane. This isn't the case for elements (such as EPs) that are close to
the focal plane (or secondary focal plane, such as your retina).
_________________________________________________
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com
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Date: 26 Jun 2007 18:47:03
From: mitch
Subject: Re: I'm Sold !
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Well, the whole point of the cloudy nights article makes the powermate clear
over
standard barlows.
>>Good point. Does that mean, then, that eyepiece/barlow aberrations are
>>less critical than objective lens/mirror aberrations? If so, why? Just
>>the much much smaller surface area?
>
> Consider what most optical aberrations are at a small scale: a ray which
> should leave a surface at some angle A actually leaves at an angle A+dA.
> That's the case whether you are talking about some huge objective or an
> internal surface in an EP. The value of dA doesn't scale with the size
> of the optic. The effect of that deviated ray, however, increases as you
> get farther from the aberrating surface. Even a small angular aberration
> at the objective can become a large linear aberration at the focal
> plane. This isn't the case for elements (such as EPs) that are close to
> the focal plane (or secondary focal plane, such as your retina).
>
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Date: 26 Jun 2007 19:02:24
From: Chris L Peterson
Subject: Re: I'm Sold !
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On Tue, 26 Jun 2007 18:47:03 GMT, "mitch" <mitch@nospam.net > wrote:
>Well, the whole point of the cloudy nights article makes the powermate clear
>over
>standard barlows.
Well, let us know how you like it. There were some technical errors in
the review (the stuff about cone angles), but that's not to say that
David didn't really like the Powermate in practice. Personally, I've
used it and am unable to see any difference in optical quality between
it and an Orion 2" Shorty barlow. But maybe with your eyes, or your
eyepieces, you will (it's no secret that I'm not primarily a visual
astronomer, after all <g >).
_________________________________________________
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com
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Date: 27 Jun 2007 02:07:53
From: mitch
Subject: Re: I'm Sold !
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Personally, I've
> used it and am unable to see any difference in optical quality between
> it and an Orion 2" Shorty barlow. But maybe with your eyes, or your
> eyepieces, you will (it's no secret that I'm not primarily a visual
> astronomer, after all <g>).
>
Ok...but what about 1.25 inchers? Your comparison isn't sound. The
2" 4 X powermate is about 100 bucks more and I bet it would
blow your Orion out of the water.
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Date: 28 Jun 2007 00:13:17
From: KLM
Subject: Re: I'm Sold !
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mitch wrote:
> Personally, I've
> > used it and am unable to see any difference in optical quality between
> > it and an Orion 2" Shorty barlow. But maybe with your eyes, or your
> > eyepieces, you will (it's no secret that I'm not primarily a visual
> > astronomer, after all <g>).
> >
>
> Ok...but what about 1.25 inchers? Your comparison isn't sound. The
> 2" 4 X powermate is about 100 bucks more and I bet it would
> blow your Orion out of the water.
Prove it.
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Date: 28 Jun 2007 05:20:26
From: mitch
Subject: Re: I'm Sold !
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"KLM" <milk@parishilton.com > wrote in message
news:4683436D.43C57BC6@parishilton.com...
>
>
> mitch wrote:
>
>> Personally, I've
>> > used it and am unable to see any difference in optical quality between
>> > it and an Orion 2" Shorty barlow. But maybe with your eyes, or your
>> > eyepieces, you will (it's no secret that I'm not primarily a visual
>> > astronomer, after all <g>).
>> >
>>
>> Ok...but what about 1.25 inchers? Your comparison isn't sound. The
>> 2" 4 X powermate is about 100 bucks more and I bet it would
>> blow your Orion out of the water.
>
> Prove it.
Use your head...
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Date: 28 Jun 2007 16:03:12
From: Dennis Woos
Subject: Re: I'm Sold !
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>>> Personally, I've
>>> > used it and am unable to see any difference in optical quality between
>>> > it and an Orion 2" Shorty barlow. But maybe with your eyes, or your
>>> > eyepieces, you will (it's no secret that I'm not primarily a visual
>>> > astronomer, after all <g>).
>>> >
>>>
>>> Ok...but what about 1.25 inchers? Your comparison isn't sound. The
>>> 2" 4 X powermate is about 100 bucks more and I bet it would
>>> blow your Orion out of the water.
>>
>> Prove it.
>
> Use your head...
Better to use your eyes, no? Of course, after spending $$$ many folks will
see what they want to see.
I am not saying that the TV Powermates aren't great (they are) but so are
many high-quality barlows. You know, I read alot of posts here and elsewhere
(e.g. CloudyNights) which seem to me to express "irrational exuberance" for
premium accessories. The bottom line is that there are no magic eyepieces,
barlows, etc., and the differences on-axis between good quality/low cost and
premium/high cost are usually non-existent. Off-axis, wide-field on fast
scopes is another matter, and this is where TV and a few others stand out.
Dennis
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Date: 29 Jun 2007 03:24:08
From: mitch
Subject: Re: I'm Sold !
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"Dennis Woos" <dpwoos@gmavt.net > wrote in message
news:13885043tbblfb1@corp.supernews.com...
>>>> Personally, I've
>>>> > used it and am unable to see any difference in optical quality
>>>> > between
>>>> > it and an Orion 2" Shorty barlow. But maybe with your eyes, or your
>>>> > eyepieces, you will (it's no secret that I'm not primarily a visual
>>>> > astronomer, after all <g>).
>>>> >
>>>>
>>>> Ok...but what about 1.25 inchers? Your comparison isn't sound. The
>>>> 2" 4 X powermate is about 100 bucks more and I bet it would
>>>> blow your Orion out of the water.
>>>
>>> Prove it.
>>
>> Use your head...
>
> Better to use your eyes, no? Of course, after spending $$$ many folks will
> see what they want to see.
>
> I am not saying that the TV Powermates aren't great (they are) but so are
> many high-quality barlows. You know, I read alot of posts here and
> elsewhere (e.g. CloudyNights) which seem to me to express "irrational
> exuberance" for premium accessories. The bottom line is that there are no
> magic eyepieces, barlows, etc., and the differences on-axis between good
> quality/low cost and premium/high cost are usually non-existent. Off-axis,
> wide-field on fast scopes is another matter, and this is where TV and a
> few others stand out.
>
> Dennis
I may be pendantic somewhat here and I may kick myself for laying out some
200 bucks for this but as the old adage goes...you get what you pay for.
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Date: 29 Jun 2007 10:49:19
From: Dennis Woos
Subject: Re: I'm Sold !
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>> I am not saying that the TV Powermates aren't great (they are) but so are
>> many high-quality barlows. You know, I read alot of posts here and
>> elsewhere (e.g. CloudyNights) which seem to me to express "irrational
>> exuberance" for premium accessories. The bottom line is that there are no
>> magic eyepieces, barlows, etc., and the differences on-axis between good
>> quality/low cost and premium/high cost are usually non-existent.
>> Off-axis, wide-field on fast scopes is another matter, and this is where
>> TV and a few others stand out.
>>
>> Dennis
>
> I may be pendantic somewhat here and I may kick myself for laying out some
> 200 bucks for this but as the old adage goes...you get what you pay for.
I think you would find it useful to go to www.televue.com where you will
find write-ups on both TV Barlows and Powermates. One advantage of the
Powermate explained there is that it preserves the eye relief on long focal
length eyepieces. I have found unacceptable the increased eye relief of a TV
32mm Plossl paired with a 1.25" 2x TV Barlow, and it may be that the
Powermate would do a better job. A friend of ours has a couple of
Powermates, and I am going to see if they do in fact handle the 32mm Plossl
better than a Barlow.
Dennis
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Date: 29 Jun 2007 04:13:20
From: Chris L Peterson
Subject: Re: I'm Sold !
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On Fri, 29 Jun 2007 03:24:08 GMT, "mitch" <mitch@nospam.net > wrote:
>I may be pendantic somewhat here and I may kick myself for laying out some
>200 bucks for this but as the old adage goes...you get what you pay for.
Sometimes, but not always. And even when the adage is true, the
relationship is seldom linear. With most "good" stuff, there's a point
in the curve where you start paying huge additional amounts for very
small improvements in performance.
The above comment is theoretical; I'm not making any guesses where this
focal expander fits along the curve. As I said earlier, let us know how
you like it once its been in use a while.
_________________________________________________
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com
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Date: 29 Jun 2007 06:55:42
From: mitch
Subject: Re: I'm Sold !
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"Chris L Peterson" <clp@alumni.caltech.edu > wrote in message
news:ag198358mend1b9h6qgfmdgc6dg3t2fphr@4ax.com...
> On Fri, 29 Jun 2007 03:24:08 GMT, "mitch" <mitch@nospam.net> wrote:
>
>>I may be pendantic somewhat here and I may kick myself for laying out some
>>200 bucks for this but as the old adage goes...you get what you pay for.
>
> Sometimes, but not always. And even when the adage is true, the
> relationship is seldom linear. With most "good" stuff, there's a point
> in the curve where you start paying huge additional amounts for very
> small improvements in performance.
>
> The above comment is theoretical; I'm not making any guesses where this
> focal expander fits along the curve. As I said earlier, let us know how
> you like it once its been in use a while.
Ok. But I only have my 2 X's 3-element, mid-1980ish, tele-negative Meade
model 140
to compare to. It is no slouch at all. I will keep it probably..but maybe
not.
I'm hoping for a noticeable wider field and at least significantly better
images at comparable mags.
I am certain I will get one or both.
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Date: 30 Jun 2007 05:28:39
From: David Knisely
Subject: Re: I'm Sold !
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mitch wrote:
> Ok. But I only have my 2 X's 3-element, mid-1980ish, tele-negative Meade
> model 140
> to compare to. It is no slouch at all. I will keep it probably..but maybe
> not.
> I'm hoping for a noticeable wider field and at least significantly better
> images at comparable mags.
> I am certain I will get one or both.
The Tele Vue 2.5x Powermate is better than the Meade 140, especially
when really pushing the magnification. The performance difference is
modest but is noticable, mostly in terms of a little less scattered
light and less residual chromatic aberration when used with short focal
length eyepieces. I have compared both and was quite happy that I got
the 2.5 Powermate. My 140 no longer resides in my eyepiece box. 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: 27 Jun 2007 05:50:35
From: Chris L Peterson
Subject: Re: I'm Sold !
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On Wed, 27 Jun 2007 02:07:53 GMT, "mitch" <mitch@nospam.net > wrote:
>Ok...but what about 1.25 inchers? Your comparison isn't sound. The
>2" 4 X powermate is about 100 bucks more and I bet it would
>blow your Orion out of the water.
It might be better, or might not. I don't think it would be as extreme
as you suggest. To my eyes, the Shorty is invisible. That is, I see no
image degradation compared with using an EP without it. So I have to
think that whatever differences I'd see between these two devices would
be subtle at best- probably more subtle than matters to me.
_________________________________________________
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com
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Date: 26 Jun 2007 10:33:52
From: LarryG
Subject: Re: I'm Sold !
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On Jun 26, 11:51 am, Rich <rander3...@gmail.com > wrote:
> On Jun 25, 4:30 pm, "mitch" <m...@nospam.net> wrote:
>
> >http://www.cloudynights.com/item.php?item_id=86
>
> > just ordered one. $230 CAD total
>
> I can't help thinking that for $230, I could order a negative achromat
> with "certified" wavefront accuracy from any good optical supply
> house.
> With eyepieces, barlows, etc, from telescope companies, we have no
> way of knowing what their true specs are. I've often wondered why we
> often ask for this with the telescopes, but never the optical
> accessories.
Perhaps because the wave-rating of eyepieces is simply much less
important.
If we were to expect quarter-wave optical perfection all the way
through the system, the manufacturing costs of even a fairly simple
Plossl eyepiece would be "astronomical", approaching the cost of a
modest size telescope. Eight optical surfaces would have to be
individually corrected, and then appropriately matched to meet
a needlessly stringent requirement.
And then, the observer's own vision system (eye, glasses / contacts)
would have to be corrected to quarter wave. At the moment, I am
not aware of any corrective surgery which can even hope to guarantee
any wave-front final accuracy even close to one-wave, let alone one-
quarter wave.
Of course, if you're Rich-enough, I'm sure you can afford it! ;-)
Cheers,
Larry G.
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Date: 26 Jun 2007 09:51:03
From: Rich
Subject: Re: I'm Sold !
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On Jun 25, 4:30 pm, "mitch" <m...@nospam.net > wrote:
> http://www.cloudynights.com/item.php?item_id=86
>
> just ordered one. $230 CAD total
I can't help thinking that for $230, I could order a negative achromat
with "certified" wavefront accuracy from any good optical supply
house.
With eyepieces, barlows, etc, from telescope companies, we have no
way of knowing what their true specs are. I've often wondered why we
often ask for this with the telescopes, but never the optical
accessories.
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