Quote:
Originally Posted by Renato1
The star is dead centre and it becomes a concentric doughnut without any rings.
Believe me - when I first got it I was scratching my head as it didn't do what my other reflector, refractor and C8 was doing - they all gave me rings. I immediately had to order a Cheshire.
Cheers,
Renato
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Not seeing any rings at all would not be a collimation issue here but an indication of an optical problem with the scope.
I'm no expert but a complete lack of rings is usually associated with excessive surface roughness of the mirror or an eyepiece that is very bad at your f-ratio.
Adding an aperture stop to a scope will suppress a few of it's inherent aberrations so that could explain why you are seeing the rings at the higher f-ratios.
Hope I'm wrong though...
gb.