Re: [ATM] ritchey cretians

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

Remember that the R-C is just one of the family of Cassegrain
telescopes so the procedures for makign one is pretty much the
same as any ohter.  The R0C, iof course, is the one with the two
hyperoloidal mirrors and the primary is just past the parabola,
usually by about 4-5 pwercent, while the secondary is  a lot
stronger.  The tests for a convex surface are all usable up to,
and including the autocollimation test where you run the light
from the focus of the telescope through the system and then hit a
large flat whereupon the light goes back through the system to
the tester whereupon a perfect system will show a flat surfacce
as a sphere in the Foucault test would show.
The test plate (described by another poster on this thread) also
works well for getting close to what yo need but may be a bit
more demanding of the testing phase.
Then there's the Hindle test which wants a spherical mirror of
about half of the ROC and a sphere with a hole in the middle of
for the test. You can either reuse the glass as the primary by
grinding it to the desired radius or making a fast  Newt out of
it or just using it as a part of an even faster Cass scope.
There is a limit to that idea tho!
Bob May
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