ATM 8" CCD camera considerations

[Richard Schwartz <richas@idt.net>]

Jeff, since your proposed 8" is for CCD use, you can really get away
with murder.  You do not even come close to diffraction-limited
resolution, so you don't need to worry about sucking and blowing,
central obstructions, flotations, or any of that other elitist
baloney.   In fact, you may want to consider saving money by eliminating
the diagonal.   Depending on the size of your camera, you might be able
to mount the CCD camera directly on the spider.

Once you determine the dimensions of your focal plane array and central
obstruction, you should use a ray trace program to find out how much
correction yields the best mirror.  I guess the way to go is to minimize
the maximum spot size over your field.   You may be shocked to find that
the optimum mirror is NOT a parabola!

You probably pay careful attention to elimination of stray light.  The
best light absorber is a CAVITY.   You build cavities into your
telescope tube by having an extra fat tube with baffles inside.

I know that you are planning to do an 8"; can you be talked into doing a
9"?   I would be happy to make the mirror blank for you, but if you live
in Borneo, Bengladesh, Tannu Tuva, the Sweden, or other such third world
nation, the shipping cost would be prohibitive.  If you live in southern
California, you could come over to my place and help me make your blank;
this would teach you more about glass working than you want to know.
(My hands presently have three band-aids from yesterday's work.)

. . . Richard