Re: [ATM] long focal length scope design \ Re: Cutting glass into largecircles

["Bob May" <rmay@nethere.com>]

Yep, that's me at the pole raising the scope to the right height
for the moon!
The thing to remember with cassegrain type telescopes is that the
secondary multiplies the focal length of the scope by some number
that is buried in the design of the sclope.  Numbers from three
to five or more are usually used.  The obstruction of the
secondary usually sets about the number along with thedesired
focal point.  The Naysmith setup allows for a larger freedom of
the focal point and can be used to gain a lower magnifier number.
without the enlargement of the secondary as much.
After having played with a bunch of the larger scopes at RTMC and
elsewhere,  I've come to believe that any scope over about 20"
should be built as a cass design for portability reasons.  The
problem of obstruction isn't so important with large scopes as
the resolution goes way up when doing so.
Bob May
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