judging quality of 10" mirror

I think I pushed my 10" mirror as far as I could. The conditions were both clear and steady. I was using a 3mm Zhummel EP. Since the FL = 1118mm, that would be about mag = 375X. (I had collimated using a barlowed laser.)

I was viewing Saturn almost as zenith in the early morning after the moon had set. I could see the shadow of the planet on the rings (a first for me ).

I suppose that means the mirror must be good quality -- to give that kind of resolution. Or is this pretty common for dobsonians, no matter the quality of the mirror?

Clears,
Joe

Joseph Babendreier said:

I think I pushed my 10" mirror as far as I could. The conditions were both clear and steady. I was using a 3mm Zhummel EP. Since the FL = 1118mm, that would be about mag = 375X. (I had collimated using a barlowed laser.)

I was viewing Saturn almost as zenith in the early morning after the moon had set. I could see the shadow of the planet on the rings (a first for me ).

I suppose that means the mirror must be good quality -- to give that kind of resolution. Or is this pretty common for dobsonians, no matter the quality of the mirror?

Clears,
Joe

Joe,
While it's certainly a good sign your mirror can utilize a 3mm eyepiece without degradation of the image, seeing the shadow isn't necessarily a criteria for optical perfection. Star testing, examining the intra and extra focal rings at high power, for symmetry and lack of aberration, is a much better measure of optical quality. The latter takes some time and experience but it's probably one of the best methods you can do in the field to determine optical quality.
I wouldn't get too fixated on it though, just sit back on a good observing chair and enjoy the view!