Astigmatism

[acey]

Took the primary and secondary out of my 8-inch f6 dob yesterday for cleaning - got it sorted, put back together and collimated (laser and cheshire) then star tested, only to find pronounced astigmatism (still there after a long cool-down).

I suspect I might have slightly over-tightened the retaining screws on the clips round the primary, but before taking it all apart again I just wanted to check: would over-tightening cause astigmatism? Or is there anything else I should think about first?

Andrew

[Ben Ritchie]

If it's just appeared, I think that over-tightening and pinching the mirror is the classic cause

[acey]

Cheers Ben - I'll get that primary back out and slacken it.

[John]

Cheers Ben - I'll get that primary back out and slacken it.

I had the primary / cell out of my 8" Skywatcher dob a few days ago to give it a light dust. I noticed that the mirror retaining clips are not tight on the mirror by any means - actually a tiny bit of play - I've left them like that as the scope seems to perform fine.

John