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celestron c-90 collimation question

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#1 Guest_**DONOTDELETE**_*

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Posted 20 October 2005 - 05:25 PM

Hi All,
Does anyone here know how to collimate this old OTA. I find three screws on the back but they don't seem to have an effect. Any help is appreciated.
Kirby

#2 Starman1

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Posted 20 October 2005 - 06:06 PM

I think the 3 screws on the back are to hold on the rear cell cover. I don't think the instrument is collimatable. The mirror is fixed, and the corrector screws in and out on the center body.
It might be shimmable with a complete dismantling.
What are you seeing that suggests it is out of alignment?
A lot of these never focused the stars to points, but were kind of like inexpensive binoculars, with astigmatism being the predominant focus aberration.

#3 Guest_**DONOTDELETE**_*

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Posted 20 October 2005 - 07:14 PM

Don,
What I am checking is the daylight collimating routine. By that test the rings are not concentric around the secondary and shadow. If I can improve it then i will. if it is as you say, I'll live with it. It seems like a good piece of glass, although I really don't have the experience to say that for sure. I just want it for a fast setup when I don't have the time for my xt10 eq. Plus it was free.
Thanks
Kirby

#4 Guest_**DONOTDELETE**_*

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Posted 20 October 2005 - 08:27 PM

Kirby, I think the mirror is glued or siliconed into place and as such, is not meant to be user collimitable. The screws at the front hold the meniscus and do not align. But I'm going on foggy memory...

It's possible to open the scope up without too much difficulty. Good time to relube the helical.

Cheers!

Armand

#5 dougspeterson

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Posted 22 October 2005 - 07:38 PM

Celestron will take apart and recollimate for about a hundred bucks. But it was a waste of time last year when I went through a nightmare where each time it came back it was never better, just different. I finally gave up.

It may not be collimation, but a drifted secondary. In any case they need to take it apart to fix, so same problem.


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