ATM 2nd post - first scope : ) 4.25" off axis sphere

["Sidor . Kurt" <KSidor@drc.com>]

Donovan,

If you use a 4.25" F #10 spherical mirror tilted, and off axis, I do not
think you will get very good performance.  If your 4.25" mirror was a
cored-out off axis section of a larger parent mirror, the full size mirror
would have been say about a 10" diameter mirror of 10 times 4.25" or about
43" focal length.  That would make the full size (on axis mirror) a 10" F
#4.3 mirror.  If this parent mirror were left spherical and not parabolized
it would have about 6 waves of surface deviation from the ideal paraboloid.
Your off axis portion would have about 5 waves of that error at least.
Using your 4.25" F #10 mirror as an on-axis Newtonian your mirror would only
deviate from the ideal paraboloid by about a 1/5 of a wave (@510 nM).
Despite the central obstruction this would produce a much better performing
instrument.

Good Luck!

Kurt Sidor
Mechanical Engineer
Dynamics Research Corp.
Encoder Division