help please with 8" celstron sct secondary mirror

[Altair]

Oh cant believe whats happened this morning... thought id take a look to see inside the orange cap to see the screw holes for collimation of this old scope - found it was unscrewing .... then came apart...suddenly i am holding the secondary mirror in my hand and.. there is a black tube lying inside my scope which obviously held the secondary in place..luckily its lying safely away from the mirror at the moment!. now i have to remove the corrector plate to get into the tube- i have removed the tiny screws around the outer ring around the mirror and removed the ring and noted where the spacers are around the secondary mirror but it seems so tightly fixed there.. am wondering if i need to remove the screws on the outside of the ota to enable removal of the secondary?. its looking pretty scary right now.. not sure what to do next.. at least now i know the serial number of the scope if thats any help with any advice anyone can offer me..It states its a Celestron 8 serial 900604.

If anyone has any idea what i do next please let me know!

thanks so much

Dee

[michael.h.f.wilkinson]

I have a GP-C8 from 1996 (different mount, but I presume the same optical tube). I haven't got the tube here, but as far as I can see you will have to detach the corrector plate. If I am right these are held in place by three screws. Unscrewing these should allow you to remove the corrector plate, and hook the offending item out of the tube. You then have access to the rear-facing side of the secondary mounting, and should be able to reassemble the thing.

After this, reattach the corrector plate, and collimate the secondary mirror.

Hope this helps.

[Peter Drew]

Hello Altair, a bit of bad luck there!. No need to panic though, refitting is quite straightforward. As you suspected, you will have to remove the corrector plate to reassemble the secondary mirror and black secondary shade tube. I think you have already removed the 6 screws holding the thin black corrector plate retaining ring, mark the orientation of the corrector, if the corrector plate is stuck, point the tube upwards and give it a couple of carefull raps with your hand, this usually jarrs it loose. Once this is done, the secondary components can be screwed back together trapping the corrector plate between them. There may be some identification marks on the seconday for orientation purposes, this is quite important as it defines the factory settings. (I used to do this for a living!) Good luck, but get back if any further problem.

[Altair]

Well i took it apart again and then put it back together again.. hard to see marks on the ota tube for where the corrector plate should be angled to but i found on another forum that Uncle Rod thought that most of the corrector plates serial numbers were set to 3 o clock - I wasnt so sure if it meant 3 o clock as i see it or 3 o clock as the ota lies in its fork handles ( or four candles) if u get my meaning.. oh and celestron label. on back of secondary he thinks should be the right way up - anyway thats what ive done ! Just hoping it might be right..in my case. Now just waiting a few days for a clear sky ! DOH!

[Altair]

thanks so much for advices given here/ Peter, do you happen to know if Celestron marked the tube as well for aligning the corrector plate to the little serial number? as i only saw this little number on it after it came away in my hands! and do you think the 3 o clock idea might work ? or could the correct orientation be anywhere?

thanks !

Dee still under very cloudy skies

[Peter Drew]

Altair. As far as I know, what you have deduced is probably right, even if not it will be a good starting point. SCT optics are usually assembled as sets, you can't swap them around with others if you break a component. From my experience, it seems that the manufacturers provide a best overall orientation, I was able to significantly improve several by experimenting with different orientations but you need a collimation bench to do this efficiently.

[Altair]

Thanks for your comments Peter, I just rang David Hinds about the "problem" and it appears they can help me if i am really stuck. In fact they quoted me about £70 to realign the secondary correctly and collimate which i think is not bad .. and they will clean the mirrors and secondary as well for a little bit extra.. so thats put my mind at rest. Once these clouds have cleared I will have a better idea of what needs to be done!