ATM Gregorian design

[Ari <Ari@birmingham-us.crosswinds.net>]

What are the disadvantages to a Gregorian, other than funky focal
lengths and not so compact? The ATM page (http://www.atmpage.com), under
"Optical Designs," shows :
        Coma-Moderate
        Astigmatism-Moderate
        Field Curvature-Moderate
for a Gregorian, while the Cass. shows:
        Coma-Moderate to Strong 
        Astigmatism-Slight
        Field Curvature-Strong

It seems to me that moderate vs. slight astigmatism is a small price to
pay for an easier to test secondary, lower coma/field curvature, and an
erect image. I've been following the recent threads on the subject, but
forgive me if I missed anything.

I'm very interested in hearing some more advantages to the Gregorian, or
some advantages to the Cassegranians, or some disadvantages to the
Gregorian.

Ari Friedman
There's light at the end of the Sonotube.