Re: ATM Star test

["Bryan Greer" <bgreer@fpi-protostar.com>]

Art wrote:
> I attempted to star test my freshly polished first mirror 10", F/7.
> I think there was too much air turbulence as the stars I looked at
> seemed to scatter their light with no evidence of rings.  I could,
> however, focus in and bring the light to a fairly sharp point.
> Racking in and out merely created a lot of flaring and jumping
> around. I chose another bright light and found myself
> looking at Saturn.  With a 9mm eyepiece Saturn was sharp and quite
> round and I could clearly see the space between the rings and the
> sides of the planet.  I was surprised to get this clear view with
> an uncoated mirror. Does this hold promise of a good figure or is
> it common?

Hi Art,

You should try more magnification.  300X is a good starting point for your
10", and go higher if your mounting supports it.  We have our share of bad
seeing here in Ohio, and I can't remember an evening when I couldn't discern
at least some form of the diffraction rings close to focus.  Even if the
correction is off, the rings should be apparent on at least one side of
focus.

You're on the right track...

Sincerely,
Bryan Greer