8 replies to this topic

[ColdNights]

The astronomy club I belong to has an older Celestron 8” SCT (probable acquired in the 1980’s).  While taking it apart to flock the interior and clean the optics, I noticed that the secondary mirror housing will rotate while attached to the corrector plate.  Thinking I could just twist the outside and inside parts of the housing it would screw down tightly.  However, I could not even budge the two housing pieces.  Does anyone know how to tighten or disassembly the secondary mirror.  I have not found any exploded views of the secondary mirror’s components nor any YouTube videos that address the removal of the secondary mirror for this telescope.

Hope someone can respond to this post.

Thank you,

Jerry

[SomeDoSomeDont]

This book might help,    https://www.goodread...the-early-years

  

Also available in PDF format

Edited by SomeDoSomeDont, 07 March 2025 - 02:49 PM.

[dswtan]

The Starizona Hyperstar conversion docs and videos might help you a lot in dismantling the secondary:

 

https://starizona.com/pages/downloads

 

HyperStar Conversion Kit Instructions

•     HyperStar Conversion Kit
•     Conversion Kit Addendum
•     YouTube Video Instructions

 

[ColdNights]

Thank you for the replies.  I will check the links out.

Jerry

[davidmcgo]

The two halves of the secondary holder screw together but they seem to glue the threads.  The plastic ones you can usually flex the baffle a bit to break the glue.  The metal ones, I still need to figure that out since my C14 is a bit loose in the corrector but hand force won’t free the threads and I hesitate to try strap wrenches that near the corrector plate.

 

Dave

[ColdNights]

Thanks for the input.  I will not try to tighten it, but when collimating soon, I might have to rotate the item if I cannot get collimation with just the screws.  After collimation it should be left alone as it will not rotate on its own.  I did view the video about the flex technique to break the glue.

Jerry

[deSitter]

I would think this may work to your advantage - you can collimate the secondary independently of the primary using a laser and rotating the secondary and making sure the return doesn't wander.

 

If the return doesn't wander, the relative orientation of the secondary beomes moot. You can then collimate with the primary alone, a great advantage.

 

-drl

Edited by deSitter, 08 March 2025 - 02:54 PM.

[Kasmos]

There were others I can no longer find but this is a good reference for disassembling C8s.

 

https://ngc1514.com/...n/disassem.html

 

Some additional ones are in this post:

 

https://www.cloudyni...n-c8/?p=9787000

[ColdNights]

Sadly, nothing seems to work to loosen the secondary mirror’s inner shield.  With the corrector plate out of the telescope I have tried hot air gun, squeezing the inner shield, bare hands and rubber strap wrench.  I sent an email to Celestron’s tech help and hope they reply.  If it cannot be loosened or tightened, then maybe a small drop of Thin CA at that cork gasket would aid in stopping it from being rotated by hand.  Probably need to have the corrector plate out of the telescope and in a horizontal position to apply the CA.  Not sure I even want to try the CA at all.  It does not appear to rotate during use, but sometimes the stars do get fatter, but that could be from temperature change.  I do not think it is from a mirror flop, since it is on one target for many minutes.  I have ordered an EAF for the telescope to replace the manual electric focuser it currently has.  When you are taking pictures, one usually does not stick around to watch each picture.