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Cleaning up an Early 70's C8

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#1 Guest_**DONOTDELETE**_*

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Posted 04 November 2005 - 07:47 PM

I inherited an early 70's Celestron C8 with wedge, tripod, etc...it's in good shape, but I'd like to get inside and clean up the mirror and inside surface of correcting plate. There are 8 hex bolts running parallel to the tube's axis and I've removed those. But I can't seem to get the correcting plate off - that is, open it up so I can clean in there. Maybe I'm going about this much too hastily. I haven't done any damage yet I don't think - thought I'd check and see if anyone could give me some advice before proceeding.
Thanks!!!

#2 Rcade

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Posted 04 November 2005 - 08:00 PM

I have taken my corrector plate off several times.

Position the OTA so that it is veritcal and the corrector plate is pointing up.

Remove the front cover if you have not already done so.

Remove the small screws that hold the ring that retains the corrector plate. Remove the retaining ring.

Mark the position of the corrector plate relative to the OTA. I use tape on the OTA with a line on it and a small piece of tape on the secondary cover with an arrow pointing to the line on the tape on the OTA. It is important to maintain the same corrector plate orientation to the OTA (primary mirror).

Notice that there are several small spacers that look like paper around the edge of the corrector plate. Mark where they are so you can re-install them in the same places.

Be VERY CAREFUL when you remove the corrector plate. It is VERY brittle and easy to break. Remove the corrector plate by GENTLY lifing the secondary holder straight up off of the OTA.

Put it back in the same position by reversing the steps above.

Do NOT OVER TIGHTEN the small screws. Remember the corrector plate is very fragile.

I hope that this helps. Sometimes if the corrector plate has never been removed it can be stuck. GOOD LUCK !!!! :waytogo:

#3 davidmcgo

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Posted 05 November 2005 - 12:45 PM

Hi Rob,

In the old C8s from that period it was common for the corrector to get stuck to the cork gasket it sits against in the cell. No easy way to get it out, what Roger Tuthill told me once was that he used to tape the lens cap on and point the scope upwards, then blow hard into the back of the tube! Can't say I recomment trying that, but if it does not have the anti reflection coatings on the corrector, you could put a small piece of double sided foam tape on to try to pull up one side of it that way. Once the corrector is out, Goo Gone should get the tape off.

I had tried the suction cup handles used for lifting glass from picture frames on an even older scope that Celestron would not work on any more (1965 C10) but my corrector slid sideways off them and only the dumbest of luck saved it from breaking. I didn't have a choice but do it myself since Celestron wouldn't service optics they could not replace. You still have the option of sending your scope in to them to work on, and on my 1976 C8 as well as an orange C5 and C11 they did the full starbright coatings and really made everything new.

Dave

#4 Rcade

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Posted 05 November 2005 - 04:40 PM

I know that the corrector plate can get stuck and be difficult to remove, especially on the older OTAs. To me the trick is getting it to give without breaking the brittle glass. Sometimes a good rap on the side of the front of the scope will work but again you risk dropping the corrector when its bond does give. I never thought of blowing in the OTA, cleaver idea. But again I would want some one there to catch the corrector plate when it does come loose.

Good luck

#5 Guest_**DONOTDELETE**_*

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Posted 05 November 2005 - 10:42 PM

Hey guys, thanks a lot for your helpful comments! When I had written that post, all I had done was to remove the eight small screws around the ring and like you all said - nothing would budge... it's definitely stuck there. Well, to be honest, I'm not going to try and do it myself. I'd feel horrible about breaking the corrector plate. I can't believe that Celestron will work on it for me - I wonder what they'd charge me! I'll give them a call Monday and find out.
Thanks again for your help and advice!

#6 Guest_**DONOTDELETE**_*

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Posted 06 November 2005 - 07:39 PM

Rob,
I was able to take apart my C8 successfully using the instructions at this link.. http://ngc1514.com/C...on/disassem.htm
It ended up being fairly easy and I was able to clean up some 20 years of accumulated grime. Scope is fantastic now. If Celestron prove to be more expensive than you hope for to do the work, the above instructions worked for me.
cheers,
David


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