Re: ATM 16" f/3.9 considerations

["Chuck Hards" <chuckh@companionsystems.com>]

I agree with Mel on a tiny circle of 100% illumination.  Too, if you were to
go with a larger circle of 100% illumination of larger size, the secondary
"shadow" may become objectionably large with low-power eps.
I built an 8" f/3.75 several years ago, and adopting a 100% circle of 0.5"
resulted in a very noticable secondary shadow.  Also this scope (built for
another person; he wanted to use a 35mm camera with as little vignetting as
possible, as well as visual, thus the 0.5" compromise) does not like most
wide-field eyepieces.  Coma is bad at low powers.  TV claims their eps work
as advertised at f/4, so maybe f/3.9 is close enough.  f/3.75 sure isn't.

Chuck