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Equipment Discussions >> Classic Telescopes

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Joe Cepleur
Carpal Tunnel


Reged: 03/18/10

Loc: Dark North Woods
Re: Is this Celestron C90 "Classic" or "Used?" new [Re: actionhac]
      #5539909 - 11/26/12 07:54 AM

Quote:

Now here's a good idea:
http://www.cloudynights.com/ubbthreads/showflat.php/Cat/0/Number/5475652/Main...

Robert




Yes, Actionhac; thanks, that's slick! Funny to see that adapter used successfully, since I could not get the scope to focus with even the added back focus of a 0.965"-to-1.25" adapter. I'll have to try again. Alternatively, since the scope needs a new hybrid diagonal anyway, does anyone make one with a built-in, helical fine focuser?


DREAMING OF ASTRONOMY -- LEARNING IN MY SLEEP

I dreamed last night about the images of Jupiter and the Orion Nebula seen through the scope. They answered the question about the relationship between resolution, brightness, and contrast.

Other than the trouble getting the scope to focus, images seemed sharp and detailed. That is "resolution."

The Moon was bright, so conditions were not ideal. Still, the sky and my targets were brighter through the scope than with the naked eye, a function of "brightness."

Trouble was, stars did not pop against the background, the cloud bands of Jupiter were barely discernible, and the nebulosity surrounding the Orion Nebula, while impressive for so small a scope, did not extend further into the sky. These were problems of "contrast." The image was however bright, but the difference between the brightest and darkest parts of the image was insufficient to make observed objects pop. Still, the view was pretty good for a scope that weighs almost nothing, and is small enough to carry anywhere! Presumably, this is the quality that would be most improved by trading the little Mak for a refractor or off-axis reflector. The contrast would be more suitably appropriate to the other qualities of the view. It was likely good luck for my understanding that I tested this on a moonlit night, when this issue would be at its worst. The views would be much better, and the importance of contrast less obvious, in dark skies.

In sunlight, it's a different story altogether. I'm still impressed with the detail seen on objects between half a mile and a mile-and-a-half away. I can see why birders love this scope without reservation.


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actionhac
Post Laureate
*****

Reged: 08/09/08

Loc: Seattle
Re: Is this Celestron C90 "Classic" or "Used?" new [Re: Joe Cepleur]
      #5540092 - 11/26/12 10:59 AM

I like that idea too. It does solve the problem of the camera lens style focusing which is the only thing I don't like about the C90 for astro work. Now for action like animals, sports etc. the camera type helical is great because of its speed and you can hold the C90 like you would a SLR camera.
I guess I need to go to a hardware store and look at the plumbing section.

The contrast problem is probably the secondary obstruction. with any CAt or Mak I feel like I forgot to take my sunglasses off.
I have done side-by-side tests with my C8 and Optical Craftsmen 8" Newtonian and the difference is very obvious, especially the Orion Nebula.
But this is one of the sacrifices we make to have such a compact instrument. Sometimes I'm willing to give up some precious contrast. When I want to observe seated the C8 is great. Just imagine taking a 60X1000 refractor to a baseball game.

Robert


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Ducky62
professor emeritus


Reged: 10/31/10

Loc: The ATL
Re: Is this Celestron C90 "Classic" or "Used?" new [Re: Joe Cepleur]
      #5540093 - 11/26/12 10:59 AM

Large Accessory Ring. It is the Celestron part that allows the use of 1.25" accessories. I don't know if the Meade one fits later C-90s.

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Joe Cepleur
Carpal Tunnel


Reged: 03/18/10

Loc: Dark North Woods
Re: Is this Celestron C90 "Classic" or "Used?" new [Re: actionhac]
      #5540193 - 11/26/12 11:59 AM

If the C90's mathematics say it should have the contrast of an unobstructed 60mm, why are the dimmer images of Jupiter's cloud bands through my Jason 313 so much more vivid and beautiful? So much for theory. It's as though the view through the C90 was washed out and overexposed. Still, at the right price, it's a tempting keeper for birding, or for astronomy from the trunk of the car. It's just so perfectly portable.

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Geo.
Carpal Tunnel
*****

Reged: 10/01/08

Loc: Upstate NY
Re: Is this Celestron C90 "Classic" or "Used?" new [Re: Ducky62]
      #5540424 - 11/26/12 02:33 PM

Quote:

Large Accessory Ring. It is the Celestron part that allows the use of 1.25" accessories. I don't know if the Meade one fits later C-90s.




Fits some, tight on others. I've found the helical focuser's action is much better on the later C90's. The early black tubes in f/11 and f/5.6 were for use as camera lenses and were not coated. The OT C90s had a coated menicus. Probably why this post OT period specimen is denoted as special coatings, meaning it was intended as a scope not a lens.


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Joe Cepleur
Carpal Tunnel


Reged: 03/18/10

Loc: Dark North Woods
Re: Is this Celestron C90 "Classic" or "Used?" new [Re: Geo.]
      #5540620 - 11/26/12 04:30 PM

Quote:

The early black tubes in f/11 and f/5.6 were for use as camera lenses and were not coated. The OT C90s had a coated menicus. Probably why this post OT period specimen is denoted as special coatings, meaning it was intended as a scope not a lens.




Are you saying that all orange tube C90s have the equivalent of "Special Coating," despite not being labled as such? That's interesting, because one of the posters above said he did not know whether his orange tube was coated.


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greju
Carpal Tunnel
*****

Reged: 10/13/05

Re: Is this Celestron C90 "Classic" or "Used?" new [Re: Joe Cepleur]
      #5540700 - 11/26/12 05:24 PM Attachment (29 downloads)

*** "Classic" or "Used?" - Used

*** Torrance, Vixen Japan, or China? - Not enough info

*** What might it be worth? - Alot of acc's and nice case, $150.00-200.00

*** Lucky find, or best to pass? - Only you can say, it is not a "classic" and it is not really made for astronomy. Might have good optics though.


I prefer the ones that still used "International" in the name. And a LAR that is the real deal. Try finding one for $25.00 though.


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greju
Carpal Tunnel
*****

Reged: 10/13/05

Re: Is this Celestron C90 "Classic" or "Used?" new [Re: greju]
      #5540702 - 11/26/12 05:27 PM Attachment (29 downloads)

It has been said the optics on the early ones are comparable to Questar. I know they are good.

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Joe Cepleur
Carpal Tunnel


Reged: 03/18/10

Loc: Dark North Woods
Re: Is this Celestron C90 "Classic" or "Used?" new [Re: greju]
      #5540733 - 11/26/12 05:57 PM

It would be clearer of me to photograph scopes with only the parts included in the sale. This one actually sells with no accessories other than the case, the lens cap, the yellow rubber cover for the back, and the finder. The diagonal, eyepieces, and tripod are mine. How much does that change the notion of a $150 to $200 value?

No question, this is a birding scope suitable for only basic astronomy duty. It would be suitable for carrying to birding sites, and perhaps for carrying about the yard, dodging the many trees, practicing finding objects already seen in binoculars.

I was out with it this afternoon, testing it on boat houses across the lake 3/4 and 1 1/2 miles away, and was surprised to find myself watching loons stretch their flippers out of the water. Their molting plumage was clearly changed from breeding to winter. Pretty amazing for so small a scope!


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actionhac
Post Laureate
*****

Reged: 08/09/08

Loc: Seattle
Re: Is this Celestron C90 "Classic" or "Used?" new [Re: Joe Cepleur]
      #5540910 - 11/26/12 07:52 PM Attachment (30 downloads)

Here I am about to do some sky sweeping for targets. (once it gets dark of course!)Anything I stumble across is game for a check out look see. It can get fairly exciting if I catch a satellite and track it. This set up is probably the favorite thing I do with my C90. Wide field 25mm eyepiece for around 40X. You will notice I have no finder, I'm not trying to find anything. I just want to be lost in space!

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Joe Cepleur
Carpal Tunnel


Reged: 03/18/10

Loc: Dark North Woods
C90 is "Used" Indeed! Missing the Visual Back. new [Re: Joe Cepleur]
      #5540911 - 11/26/12 07:52 PM Attachment (33 downloads)

Please could someone confirm that the photograph below shows the problem with this scope?

The seller told me that the man who sold it to him had "drilled it... to accept 1.25" eyepieces, or something like that... there are problems with it." The scope has two holes drilled near each other at the end of the baffle tube. One of them has a retaining screw, for gripping a 0.965" diagonal from a refractor. That's the problem! The C90 requires a SCT-style visual back that screws onto the threads on the outside of the baffle tube. A refractor's diagonal is too small when stuffed in there, and so is both off-center and wiggly. The result is a miscolimated scope with weird vignetting at low powers, that never quite focuses correctly, and has a cat's-eye shaped field stop.

Is the visual back for this scope readily available, or an expensive rarity on the used market? Ducky62 so valued the...

Quote:

Large Accessory Ring... the Celestron part that allows the use of 1.25" accessories.




because that's an even better option.

Probably someone bought this as a camera lens (judging by the cutouts in the case), and then later decided to convert if for astronomy, but did not know how to do it right. The optics can not be properly tested without the right visual back, which surely lowers the price I'd pay.

Anyone know where I might buy a visual back or Large Accessory Ring, and how much it might cost?


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Ducky62
professor emeritus


Reged: 10/31/10

Loc: The ATL
Re: Is this Celestron C90 "Classic" or "Used?" new [Re: greju]
      #5540913 - 11/26/12 07:54 PM

Quote:



I prefer the ones that still used "International" in the name. And a LAR that is the real deal. Try finding one for $25.00 though.




You're not helping on the future availability of affordable LARs

Quote:

I'd add at least $25 for a LAR




I was trying to be a bit more subtle


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Joe Cepleur
Carpal Tunnel


Reged: 03/18/10

Loc: Dark North Woods
Re: Is this Celestron C90 "Classic" or "Used?" new [Re: actionhac]
      #5540918 - 11/26/12 07:57 PM

Quote:

Here I'm about to do some sky sweeping for targets. (once it gets dark of course!)Anything I stumble across is game for a check out look see. It can get fairly exciting if I catch a satellite and track it. This set up is probably the favorite thing I do with my C90. Wide field 25mm eyepiece for around 40X.




Love it! That's exactly the setup I'd like for trotting about the yard. I see a well-mounted C90 not as a substitute for a C8 or even a classic refractor, but rather as a kind of uber-monocular that combines almost the convenience of binoculars with a much steadier view and higher powers.


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Joe Cepleur
Carpal Tunnel


Reged: 03/18/10

Loc: Dark North Woods
Re: Is this Celestron C90 "Classic" or "Used?" new [Re: Joe Cepleur]
      #5540924 - 11/26/12 07:59 PM

So, I need a LAR and then the same visual back I'd use on a C8. Suddenly, this scope has gotten expensive. I'd have to buy it at a bargain-basement price.

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actionhac
Post Laureate
*****

Reged: 08/09/08

Loc: Seattle
Re: Is this Celestron C90 "Classic" or "Used?" new [Re: Joe Cepleur]
      #5540961 - 11/26/12 08:17 PM Attachment (34 downloads)

Here's a picture of mine Joe, does this help?

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actionhac
Post Laureate
*****

Reged: 08/09/08

Loc: Seattle
Re: Is this Celestron C90 "Classic" or "Used?" new [Re: actionhac]
      #5541053 - 11/26/12 09:11 PM

Joe from what your describing I wonder if the baffles have a problem.
Look at this site and go to regluing light baffle and also look closely at the end of the baffle tube in the pictures and compare to yours:
http://astronomyasylum.com/c90.html

Robert


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Joe Cepleur
Carpal Tunnel


Reged: 03/18/10

Loc: Dark North Woods
Re: Is this Celestron C90 "Classic" or "Used?" new [Re: actionhac]
      #5541139 - 11/26/12 09:55 PM

Quote:

Here's a picture of mine Joe, does this help?




Let it be shouted from the rooftops:

*** JOE CEPLEUR WAS WRONG!!! ***

Your picture clearly shows the same configuration as mine. Same set screw in same place. No aftermarket, kludging debauchery wrecked my scope. Do you slip a 0.965" diagonal in there, the same sort that fits a classic refractor, and secure it with the set screw? or do you screw a visual back to the threads?

Okay; I was partly right. My diagonal is floppy, and that was a problem. Would an ordinary hybrid diagonal solve my problem? or would I be better served to find and screw into place a proper visual back?

Crawmach could machine a LAR, but custom work is pricey.


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greju
Carpal Tunnel
*****

Reged: 10/13/05

Re: Is this Celestron C90 "Classic" or "Used?" new [Re: Joe Cepleur]
      #5541147 - 11/26/12 10:02 PM

Depends on how much you want to spend. A hybrid diagonal should work fine with the set screw. I wasn't seeing your "problem". Turns out there wasn't one. Great!

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greju
Carpal Tunnel
*****

Reged: 10/13/05

Re: Is this Celestron C90 "Classic" or "Used?" new [Re: Joe Cepleur]
      #5541170 - 11/26/12 10:14 PM

Looking at yours there is that extra hole in the visual back and if your diagonal does not fit tightly some type of "debauchery" could have been done there. The diagonal that came with mine is not a SCT screw in type and fits in there snugly.

Edited by greju (11/26/12 10:17 PM)


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Joe Cepleur
Carpal Tunnel


Reged: 03/18/10

Loc: Dark North Woods
Re: Is this Celestron C90 "Classic" or "Used?" new [Re: actionhac]
      #5541174 - 11/26/12 10:18 PM

Quote:

Joe from what your describing I wonder if the baffles have a problem.




Good thought, thanks, Robert; but, alas, the light baffle is not rattling around inside.


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