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Originally Posted by glend
I pulled the primary mirror out of my GSO 12" dob yesterday to give it a clean and to install my upgraded springs. I marked the mirror on the sides of the support clamps so that I could put it all back together correctly. After getting it all back together I did a laser collimation and tested it out last night. It's great at lower power but when using the 9mm and 6mm higher powered eyepieces I am getting short astigmation tails that extend out to the 2pm position (on the image as seen in the eyepiece). I am assuming that one or more of my mirror clamps is probably to tight; is this a correct assumption? I did a star test and my donut appears to have a bite out of it on the right side (of the image). I did not attempt to fix it last night because the clamps require disassembly, and I didn't want to tackle that in the dark.
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Flaring is likely to be caused by one of the primary clips too tight. Astigmatism is another thing altogether and usually induced by the secondary, not the primary. It is obvious when you go in focus and out focus. The pattern of the diffraction rings will become oblong and rotate 90 degrees on each side of focus, so at focus point you won't get a pinpoint star but a somehow blurry cross. Sometime the secondary is pinched and causes that. Otherwise 90% of the time you can fix this by rotating the primary until you find a spot where it's gone.
Quote:
Originally Posted by glend
Secondly, at the back of the mirror where it sits ... which is what I tried to do?
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Can't help you with that. Others will chime in.
Quote:
Originally Posted by glend
Finally, GSO (in their wisdom) make both the adjustment knobs and locking knobs the same thread size so it is possible to mis-align the frame in the carrier when remounting the springs. Am I correct in that the locking knobs only go through the holes where only one side is threaded and thus push against the internal mirror support frame to lock it in place; and the spring knobs screw into the internal mirror support frame? Or do I have it wrong way around?
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The locking knobs are threaded on the top ring and push against the mirror cell. The collimation knobs are threaded into the primary mirror cell (the one with the clips) and are spring loaded against the top ring. Once collimated the three locking knobs just need to touch the cell to stop it from moving. No pressure is needed. Ideally locking knobs should be right next to the collimation screws for an efficient push/pull system. Not sure why GSO stuck them in the middle.