Re:ATM Cassegrain as second telescope project.

[Michael Peck <mpeck1@ix.netcom.com>]

At 08:29 8/6/2002 -0400, William Mc Hale wrote:
>Correct me if I am wrong, but the coma in a Cassegrain is the same as a
>Newt of equal f/ratio.  Since coma in a Newtonian is negligable for most
>

Assuming you're talking about a classical Cassegrain, you're not wrong. For 
something like an f/4 primary, f/15 system field curvature is the most 
important field aberration, followed by astigmatism. Coma is barely 
noticeable in a classical Cass. What Kevin is proposing (say, f/3 primary 
and f/18 overall in a RC design) will increase field curvature while 
eliminating an already tiny amount of coma.

There are other considerations, like secondary size, conic constants, and 
total amount of glass that needs to be removed. Except for secondary size I 
don't see an obvious reason not to favor the more conservative design 
though (i.e. the one Suzy had in mind).

Mike Peck


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Michael Peck
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