secondary mirror dropped off SCT help!

[philip57]

Hi.

I am in a bit of a mess. I installed bobs knobs on my SCT Celestron 9.25 and was collimating and the secondary mirror dropped off inside the OTA. Luckily it caused no damage to the corrector plate but i havent a clue how to replace this secondary mirror. I presume the corrector plate will have to be removed. Any help would be really appreciated.

Philip

[Peter Drew]

What bad luck phillip. However, it's not the end of the world, or your scope. What you will have to do is remove the corrector plate. First you remove the 6 or so screws that hold the retaining ring that has the scope specs engraved on it. Next, mark the orientation of the corrector plate relative to the tube, this is important, also take note if there are any packing pieces between the edge of the corrector plate and its cell, if there are, they will need to be replaced afterwards in the same position. The corrector plate can now be removed, these are sometimes a bit stuck and may need a couple of hand smacks to the side of the tube to release it. I presume when you say the secondary has fallen off you mean the whole assembly and not just the mirror, if so, just back off the Bobs Knobs and reconnect the central fixing screw. After reversing the whole procedure, the secondary will need recollimating.

Hope this helps. .

[Doc]

This is very unusual for this to happen, when replcing the screws for Bob's knobs you did replace one at a time not remove all three together.

[Mr Spock]

If it's a Fastar you can undo the locking ring and pull out the whole Fastar assembly. That should allow you enough room to pull the secondary out.

This is what I did when I tried to put a 1¼" cap on a 2" diagonal. Guess where it went!

[Merlin66]

The C9.25 is not fastar compatible.

[Mr Spock]

The C9.25 is not fastar compatible.

Yes it is, I own one...

[mcrossley]

I doubt a 9.25" Fastar will have a big enough secondary to get your hand in!?

If you remove the corrector, please mark the edge and the corrector casting so you can get it back in the correct orientation.

The secondary also has to go back in the correct orientation. It will have an alignment marker pen line on the back of glass - not always easy to see, but is should be there. This is normally aligned with the Fastar alignment pin.

My C14 page may give you some help: C14 Modifications

[Merlin66]

Hmmm it would appear from some discussions on CN that C9.25 delivered from Nov last year may be Fastar compatible - you need to check the precise model...

I stand corrected!

(Originally it was said that the size of the secondary mirror was larger than the hole in the corrector so could not be removed a la Fastar)