Quote:
Originally Posted by multiweb
Minute adjustments in the primary tilt can have a big influence on collimation. In my experience close enough is good enough. Where possible I've always avoided to change the primary tilt usually set at the factory.
If I had to do it then it was always a mechanical adjustment, not optical.
Tell tale of a misaligned primary is usually astigmatism and oblong on axis stars.
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Marc, I have checked both mechanical and optical alignment, and did use the reflected donut technique to adjust slight tilt anomaly. I have not noticed any astigmatism, and star shapes are round at focus, but I do still have a little coma to tune out. I agree it should not be touched, normally, but it is unclear to me what GSO does at the factory in regards to setup. I doubt they test it through the focuser, as they are known to have a slight tilt induced in that mechanical alignment, due to the way they do the threads on the mirror back plate (discovered originally by RC owners). Still it looked ok on first star testing, but showed significant concerns when bench tested, like primary tilt, off centre spot laser, etc.. I have faith in GSO mirror engineering, it is the mechanics that concern me. Sort of like they put together a couple of mechanical tweaks to get the optimal optical result, but they don't stand up to mechanical scrutiny.
I will continue to star test as conditions permit, but I was stopped last night because of sky conditions prevented higher power testing. As far as I managed to get using low power EPs it was ok, but I admit that my one old, good eye, maybe not the best judge.