Re: [APML]: Evaluating sharpness of SCTs through photographs

[Michael Covington <mcovingt@aisun1.ai.uga.edu>]

> Is there a way of evaluating the sharpness of SCTs through photographs?
> I would assume that the more pinpoint the fainter stars, the better the
> optics. The less soft the star images, the sharper the optics. 

Well... that mainly tells you how accurately the photographer focused
and guided, and how steady the air was.

> There
> must be some way to evaluate just how sharp. For instance, I have a
> Celestron Ultima, and I have compared pictures taken with various Meade
> SCTs (LX200, etc, as well as the plain C8 with no coatings). My images
> seem at the high end of quality. I know that there are also focusing
> issues involved. Any ideas?

It may be that your technique is especially good (do share it with us!).

You can do visual star tests, on nights of very steady air only, to
judge the quality of SCTs.  Both of my SCTs (C5 and Meade 2080) had
astigmatism and went back to the factory this year for new optics.
The C5's problem turned out to be that the secondary wasn't glued in
the center of the little disk that holds it!  Presumably the glue softened
and shifted over the years.

-- 
Michael A. Covington                http://www.ai.uga.edu/faculty/covington/
Artificial Intelligence Center                                           <><
The University of Georgia                Unless specifically indicated, I am
Athens, GA 30602-7415 U.S.A.                not speaking for the University.