Quote:
Originally Posted by Startrek
I can only let you know what I experienced with my 6” f6 newt 6 months ago
My stars were tight ( not eggy or oval ) but flared out a bit like a torch on the right hand side and it was worse towards the right hand side off axis area of the image
Long story short it was collimation, secondary was out and primary cork pads had compressed on 2 sides
Stripped it down , replaced the pads with thicker ones and re collimated using a Cheshire and 2 laser collimators
Problem fixed , although the scope did suffer a bit from coma which I knew about
If your image has oval or eggy star across the whole image is guessing it’s your mounts tracking even at short subs
Don’t know if this helps in any way
Cheers
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Thanks Martin :-) I use (all catseye) a cheshire for primary collimation and the off-axis pupil of an auto-collimator for secondary. I'm pretty confident of primary collimation but suspicious of the secondary.
I've been thinking about replacing the cork pads with something else after I found the mirror stuck to them once which (I think) was causing astigmatism, but I've never gotten around to it. Might just replace the entire cell at some point.
I doubt it'll be tracking with 1-5sec exposure on a very well aligned, pier-mounted Mach 1 so I think I'll be able to cross that off the list pretty easily. I think I'll also see the elongation switch direction as I shift focus, so I'll test that up front.