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07-05-2008, 10:13 AM   #16
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Lowell,

How is the collimation on your C90?

07-05-2008, 01:27 PM   #17
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QuoteOriginally posted by Blue Quote
You took my statement way out of context. I was only discussing the Celestron C90 and C5 lineage of spotting scopes. I was also referring strictly to their Schmidt Cassegrain telescope, Maksutov Cassegrain Telescope lens. The three spotting scopes that I mentioned are infact developed from their Astro telescope line. I'm not very falmiar with Swarovski Optik, but the only scopes I've seen of theirs were straight potting scopes. But since you brought it up, I don't much care for Pentax spotting scopes since Bushnell serves the purpose better for standard spotting scopes. Zeiss is good but way over priced and not their focus. If I were to go with a sporting spotting scope, I'd probably go with the Bushnell Nature or Discoverer series.

Back to the point, The c90 mak is 90mm in diameter, the C130 is 127mm in diameter (5.1"0)and the C5 is 5" in diamter. There full blown Schmidt scopes range from 6", 8", 11" and all the way up to observatory scopes. It really irks me when people see one of those Five and Dime toys with celestron or meade on it and assume that is their real stuff.

Besides, if I were going to drop $2000 or more grand on a scope, it definately would be in the 11" range! If it were primarily for camera use, and had the money, I would go for long Pentax * glass.
Ha, ha - no seriously, if I would buy Celestron (which I don't do, for various reasons), the old C5 and its photo lens derivate would be my first choice. I'ld never buy the extremely slow current modells. I also find the Celestons quite nice scopes, though I porbably will never buy a Schmidt-Cass, because I prefer other constructions, mainly classical Cassegrainians.

In my observatory I use a Lichtenknecker 3000/250 Cassegrain and a Zeiss 2250/150 Cassegrain as main instruments. For wide field a small 600/100 Semi-Apo serves well (up to 100x mag.) and the Pentax is primarily my travel scope, because you can unscrew it right in the middle and than have two tiny tubes, which you can carry easily. Also, the Pentax has the advantage of illumination medium format and offering a fully flat field, which no Celestron, Bushnell etc. can do. You have to look for, well, Pentax for that or you have to buy a Borg + largte field flattener etc. All other scopes for medium format are way bigger. and accordingly more expensive.

And I don't think, that deriving a spotting scope from an astronomical scope is a bad thing in itself, because astro scopes have to meet much more strict quality requirements (due to the high magnifications). I am not sure, whether Bushnell even offers a real Apo modell?

Oh, did you know, that Pentax was the only vendor, from whom you could buy a 250mm Apo right off the list for many, many years (now, I think TMB has something along that line, too)? It came complete with a dedicated mount and would just fit a 6m dome. It was not exactly a bargain, at 2.5 million Deutsch Marks (a couple of years ago) -- I was tempted, but my bank manager got a laughing fitů (And the dome would have been bigger, than our house.)

regards
Ben
07-05-2008, 05:54 PM   #18
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QuoteOriginally posted by Blue Quote
Lowell,

How is the collimation on your C90?
It is hard to tell. If I understand you correctly, you are meaning the axis allignment of the main mirror to the front corrective lens and secondary mirror.

I am not sure you can easily test for this.

By the way, I have checked stability, not by taking any shots but just subjectively through the view finder, and removing the rubber coating from under the lens mount has greatly improved things.
07-05-2008, 06:42 PM   #19
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QuoteOriginally posted by Lowell Goudge Quote
It is hard to tell. If I understand you correctly, you are meaning the axis allignment of the main mirror to the front corrective lens and secondary mirror.

I am not sure you can easily test for this.

By the way, I have checked stability, not by taking any shots but just subjectively through the view finder, and removing the rubber coating from under the lens mount has greatly improved things.
You would need a special eyepiece to check the collimation. I think they run ~$29.

07-05-2008, 07:05 PM   #20
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QuoteOriginally posted by Ben_Edict Quote
Ha, ha - no seriously, if I would buy Celestron (which I don't do, for various reasons), the old C5 and its photo lens derivate would be my first choice. I'ld never buy the extremely slow current modells. I also find the Celestons quite nice scopes, though I porbably will never buy a Schmidt-Cass, because I prefer other constructions, mainly classical Cassegrainians.

In my observatory I use a Lichtenknecker 3000/250 Cassegrain and a Zeiss 2250/150 Cassegrain as main instruments. For wide field a small 600/100 Semi-Apo serves well (up to 100x mag.) and the Pentax is primarily my travel scope, because you can unscrew it right in the middle and than have two tiny tubes, which you can carry easily. Also, the Pentax has the advantage of illumination medium format and offering a fully flat field, which no Celestron, Bushnell etc. can do. You have to look for, well, Pentax for that or you have to buy a Borg + largte field flattener etc. All other scopes for medium format are way bigger. and accordingly more expensive.

And I don't think, that deriving a spotting scope from an astronomical scope is a bad thing in itself, because astro scopes have to meet much more strict quality requirements (due to the high magnifications). I am not sure, whether Bushnell even offers a real Apo modell?

Oh, did you know, that Pentax was the only vendor, from whom you could buy a 250mm Apo right off the list for many, many years (now, I think TMB has something along that line, too)? It came complete with a dedicated mount and would just fit a 6m dome. It was not exactly a bargain, at 2.5 million Deutsch Marks (a couple of years ago) -- I was tempted, but my bank manager got a laughing fit… (And the dome would have been bigger, than our house.)

regards
Ben
I've never used a straight scopes for photography. The Bushnells have ED Prime Extra-Low Dispersion Fluorite glass and bak4 prisms and also have water proof models. I use them in the field and they are likely to get rained on or at the bottom of the Wacissa River. The C 90 Mak is also water proof and M. Cassegrain design so it is interesting because of it being fully water proof and the no fault warranty. But I like that C5 tube but isn't practical for field use i.e. with canoes etc. I haven't used any big scopes since college though and can only dream about a dome although I know where a used one is that I should check on.

Last edited by Blue; 07-05-2008 at 09:44 PM.
07-05-2008, 07:47 PM   #21
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Lowell, how big of a tripod and ball head are you using with the C90? Can't imagine using a ball head with a lens that big ( love ball heads and have a large Arca and larger Studio ball). Very hard to point them when head goes in all directions at once! If looking thru lens and you tap it lightly does it settle down in 3 seconds or less? Must to be able to take sharp shots. Mirror lockup is max 3 sec on Pentax K10/20D.

Had a C90 years ago. It had either single or no coating. Wasn't as sharp or contrasty as 4 year old C5 with the Starbright multicoatings. Technically larger aperture should have more resolution. My c90 was a mak. It is almost imposssible to knock them out of alignment. The C5 is a Schmidt Cassegrain. It is easy to knock out but can be aligned. Maks are built aligned and can't usually be aligned if a problem occurs.

Would love to see the Pentax spotting scope. How much, if any color fringing do they have? C5 has very little, if any. Have to try the medium format on the mirror some day.
thanks
barondla
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07-06-2008, 12:36 PM   #22
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QuoteOriginally posted by Blue Quote
I've never used a straight scopes for photography. The Bushnells have ED Prime Extra-Low Dispersion Fluorite glass and bak4 prisms and also have water proof models. I use them in the field and they are likely to get rained on or at the bottom of the Wacissa River. The C 90 Mak is also water proof and M. Cassegrain design so it is interesting because of it being fully water proof and the no fault warranty. But I like that C5 tube but isn't practical for field use i.e. with canoes etc. I haven't used any big scopes since college though and can only dream about a dome although I know where a used one is that I should check on.
The Bushnell sounds good, have never seen one of the Fluorites over here. The C5 is sure not the most practical solution for any photography that involves walking away from the car for more, than a couple of yards...

Off Topic: If you have the space and money available, don't go for a dome, a roll-off roof on a simple wooden shelter or a complete roll-off shelter is much better: better views of the sky (not the narrow dome slit) and much faster cooling times. My dome needs quite some time to cool to ambient temperatures and unless it is there, I have serious "dome seeing"... On the other other the dome gives some sehlter against stray light from street lights and neigbouring houses, which is a plus in suburban areas.

regards
Ben
07-06-2008, 12:47 PM   #23
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QuoteOriginally posted by barondla Quote
Would love to see the Pentax spotting scope. How much, if any color fringing do they have? C5 has very little, if any. Have to try the medium format on the mirror some day.
I have a dedicated Pentax astro scope - it is not primarily a spotting scope, but the constructions are similar. The Pentax astro scopes are optimized for photography, so have a flat field for 4.5x6 cm (Pentax 645 or Mamiya 645 etc.) film "out of the box". All modells above the 75mm scope are optimized right up to 6x7cm (Pentax 67, being the obvious choice). Of all the standard mirror scopes I know, only the very biggest (C14 or 16' Meade or the like), may be usable with medium format. But only if you replace the original screw mount with something, that offers a wider open diameter (Peterson Engineering has good replacements). Most medium formt mirrors are specialised astrographs, based on Newtonians with a Ross (rare) or Wynne (usually) corrector or ofcourse the goos old Ritchy-Chretiens. If you are interested, here are a few very interesting links:
Astro Optik Homepage (soory, german only, English pages under construction...)
Astro Systeme Austria
RCOS :: Home
Optical Guidance Systems Telescopes

regards
Ben

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