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Good afternoon all and hello from cloudy maidenhead!

Recently getting back into astronomy from a few years break and have just bought a Celestron cpc 800 which i love! (i used to have a 8" Dob but it was too cumbersome to take to darker skies)

Anyway as my title suggests i started\cleaning the front correction glass when i noticed the center with the collimating screws was able to rotate!? As i tried to tighten it, it kept on rotating (oh no!) This left me no choice but to remove the front glass to get inside to tighten it. I marked very carefully the exact orientation of the glass as ive heard this is matched to the main mirror and screws etc... When i removed the front end as feared the the secondary mirror was rotating also and i have no idea what position it started in! Will this just be a simple issue of re-collimating the scope or does the main and secondary mirrors need to be aligned some how?

On a second note as i had the correction glass out i decided to clean both sides of it... I cleaned it very carefully and happy with the results but the glass didn't look coated in any way, just perfect clear glass. does this sound normal?

 

Thanks for your help in advance guys

 

Stu

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The corrector does look like plain uncoated glass but it isn’t. It is coated.

There’s a good thread on the subject.of secondary mirror rotation.

 

Edited by johninderby
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Thanks that was really helpful :) 

As the secondary mirror is locked in place with the collimating screws and can't rotate can i assume that as long as I've installed the secondary housing to the corrector glass with the "faster" writing horizontal and the top collimating screw at 12 o clock this should be ok... I'm a bit nervous about removing all the collimating screws to check the back of the mirror for the alignment mark! 

 

Cheers

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I have striped it down and I Think I can see an alignment for the secondary, however I’ve checked every millimetre of the corrector glass and cannot see any marking on it what so ever. Mine is a 2010 model. I will collimate it tonight so fingers crossed ?? 

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Hi Stu.

No panic here. The outside secondary collar (where the collimating screws are) screws onto the inner secondary baffle with a gasket, therefore sandwiching the corrector plate between the two.

Removal of the corrector plate and hand tightening the secondary baffle is simple and If you realigned the secondary where it came out of (you said you had marked everything up), then there's no problem.

It doesn't matter if the secondary itself has rotated (unlike the corrector plate!), it will just need collimating again.

Hope this alleviates some doubt Stu.

 

Stu

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