ATM Alternatives to Newtonians

[Scott Rychnovsky <srychnov@chem.ps.uci.edu>]

I have been considering making a Cassegrain or one of its variants like a
Dall-Kirkham.  It sounds like an interesting project, but in the back of my
mind I have to wonder if it is really worth the bother.  For instance,
comparing a 10" F5 Newtonian with a 10" F15 Dall-Kirkham, does the
Dall-Kirkham system really have ANY advantage over the Newtonian with good
a 3X Barlow?  The Newtonian can be used for rich-field views, and the
Cassegrain variants cannot. The secondary is going to be smaller with the
Newtonian.  The field of a Newtonian is flatter, and the coma is supposed
to be the same at the same F-ratio as a Cassegrain.  Does adding the 3X
Barlow to the Newtonian give you the same coma as the F15 Cassegrain?  The
R-C variants have less coma, but they has astigmatism, and are much harder
to figure.  The tube length on an F5 Newtonian is about the same as the
tube length on an Cassegrain with an F5 primary and a 3X secondary.

Is there any situation where the Cassegrain (or its variants) are superior
to a well-made F5 Newtonian?

Scott
--
Scott Rychnovsky
srychnov@chem.ps.uci.edu