Quote:
Originally Posted by dsoscope
On slight extra focus I see a badly misshapened donut ( twice as high as it is long ) and intra focus was a perpendicular spike pattern , and on best focus, I have to settle on a triangle shaped star
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I'm guessing this is a thin mirror, right ? That is astigmatism, and it was baked in when they ground and polished the mirror. Perhaps try a Televue Dioptrix but I doubt it will help much.
Minimizing flexure during grinding and polishing - as well as in the scope - was the reason why long ago the old-school types used full-thickness mirrors, a 10" would have been close to 45-50mm thick.