collimating a SCT (CPC 1100)

[jeelan]

I tried collimating my CPC 1100 today and in mucking around with i removed the outer threaded ring holding the secondary mirror in place and moved the mirror.

Just wondering if the secondary mirror on these scopes has to be aligned in a certain way or is it ok if its been rotated? is there a screw that lines up to the top of the OTA?

Also looking at replacing the current collimating screws on the front with something of a better quality. I read on Bob's Knobs that these are an M3 screw so I'll pop down to my local fastner shop and see if they have any M3 screws with knurled knobs for better grip.

cheers
Jeelan

[multiweb]

No it cannot be rotated. Make sure its orientation is back to what it was originally. Would be a good idea to make a mark at 3 o'clock inline with the focusing knob so you remember next time.

[Greenswale]

I did that too! Scary initially.

I could not get enough movement from the screws to get collimation, so removed the secondary to investigate. Didn't see any marks. My issue was a bit of swarf in a screw thread.

I replaced the cross head screws with hex head screws, because the longer moment arm of the 'Allan key' gave far more precise control. The slightest movement of the screws has effect on collimation.

You will need an artificial star to proceed, lots on that elsewhere. You will need to start from zero, with the diagonal removed and eyeballing the image off the secondary to get it as central as possible before proceeding with diagonal and eyepiece.

Be brave!

[jeelan]

Thanks everyone - looks like i'm going to have a busy night ahead of me :-)

cheers
Jeelan

[Constant]

I am certain you will get it under control ASAP! Clear sky's

[Greenswale]

Memory strikes! Any time I was working near a mirror or the corrector plate, I wore disposable rubber gloves to keep things clean. Use only the type with no powder inside!

[jeelan]

Greenswalve I learnt that the hard way yesterday so gloves went to the top of the priority list pretty fast!!!

so i've replaced the original screws with hex heads but got some that were a little longer than the originals so had to use washers to take up the slack

http://i12.photobucket.com/albums/a227/jeelanamin/ASTRONOMY/IMG_3805_zps0khrwd5q.jpg

new screws compared to the older ones.

http://i12.photobucket.com/albums/a227/jeelanamin/ASTRONOMY/IMG_3807_zps6tpfgztq.jpg

also installed a focal reducer so should be interesting to see how that goes...

http://i12.photobucket.com/albums/a227/jeelanamin/ASTRONOMY/IMG_3808_zpsko6rwrqr.jpg

cheers
Jeelan