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Loose C8 Secondary Holder

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Posted by Tom Hudson on August 27, 2003 17:28:43 UTC

OK, while getting ready for last night's session with the scope, I was doing some reading and realized that some of the marginal viewing I had been having through my C8 may have been due to bad collimation. I have never collimated my scope, I'm embarassed to admit. I went out, popped in an ocular, found a bright star and dialed it out of focus, and sure enough, the "donut" is not nearly centered.

I grabbed some collimation instructions off the web and went out to see what I could do. I popped off the plastic cover on the secondary holder and found the three 5/64 allen screws. In my first attempt to adjust one of these, the ENTIRE secondary holder rotated! The screws were all very tight, but the rotation force to loosen one caused the whole thing to rotate. Basically, I can grab the secondary holder and wiggle/rock/rotate it. This is not good.

I rotated it while looking through the scope and the thing's clearly way out of whack. A star at the center of the field swings out of view with a partial turn. Trying to adjust the screws to alter the collimation doesn't seem to do anything; nothing tightens the secondary to the point where it is stable. I tried loosening one screw and tightening the others; but the others are already fully tight.

This is a Celestron Super C8 Plus; I've had it since probably 1987.

Some of the instructions I've seen regarding the adjustment of the secondary mirror for collimation mentions not taking all three of these screws out. Apparently, some scopes have a central screw that holds the secondary holder in place in the corrector plate. There's nothing obvious on my scope and I'm afraid to take out all three screws to see if the outside of the secondary holder comes off to reveal another screw that holds the thing to the corrector plate.

Does anyone out there know if it's possible to fix this? This is going to completely destroy my Mars imaging opportunity if this scope has to be sent in somewhere for repair. I have a complete machine shop here and am competent with just about any mechanical repair. If anyone can talk me through getting this straightened out, please contact me either on or off the list ASAP.

I can probably get the thing back in the same shape it was in before by just rotating the secondary holder but obviously having it loose is far less than optimal.

Thanks in advance, I'd really appreciate some help.

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