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I have a Celestron C8 circa 1985 that I haven't used in about 20 years. The diagonal on the finder freely rotates. There is virtually no friction, so it won't stay where I want it. I don't see any screws to tighten.

I never thought it rotated at all. Maybe it had a lot of friction and I just left it pointing up.

Can this be tightened?

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    $\begingroup$ If you don't get an answer here, cloudynights.com forums may be of help. $\endgroup$
    – Greg Miller
    Commented Apr 23 at 14:48
  • $\begingroup$ And if you do get an answer there first, it's perfectly fine to post an answer to your own question here, quote (and link to) the key points of the answer there, and even accept your own answer. $\endgroup$
    – uhoh
    Commented Apr 25 at 23:02
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    $\begingroup$ I posted on CloudyNights. They said that there should be a grub screw that holds the diagonal to the main part. I can't find any other grub screws except the two shown in the picture. $\endgroup$
    – Mattman944
    Commented Apr 26 at 1:30

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An astronomer/engineer friend helped me solve it late last night. It is simple, the diagonal screws into the front piece. The threads are very fine, so it is not obvious. It was very loose; it took about 4 turns to tighten it.

How it got so loose is a mystery. The back end can't rotate all the way around. The front end was clamped with the alignment screws.

The mercury battery for the reticle illuminator isn't available anymore. I ordered an alkaline equivalent.

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  • $\begingroup$ Congratulations! I normally wait most of the seven days before awarding a bounty, but there can be no better answer than the one that actually solves your problem! $\endgroup$
    – uhoh
    Commented Apr 27 at 11:56
  • $\begingroup$ Screws is astronomy equipment often come loose due to repeated heating/cooling cycles causing expansion and contraction. $\endgroup$
    – Greg Miller
    Commented Apr 28 at 3:02

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