Re: [ATM] Re: Aplantic Gregorian

[Jim Burrows <burrjaw@earthlink.net>]

At 2004-11-30 17:19 -0500, vladimir sacek wrote:

>"Yes one can think of such ("compensating") designs if one gives up the
>coma-free condition. One can lower the conic constant of the primary to
>get to a reasonable null focal distance..."

Let me dive in before this thread wears out.  The differential equations 
for the surface profiles of a true aplanatic two-mirror system 
(Ritchey-Chrétien or aplanatic Gregorian simultaneously satisfying the 
stigmatic and optical sine conditions) are given in Born & Wolf, 
"Principles of optics", 7th ed., p. 214-217.  The Schwarzschild conic 
formulation (Texereau, p. 147) is an approximation, the error of which is 
small, but not insignificant - about 12 nm RMS for my 10"f/8 RC cass.

         -- Jim Burrows
         -- mailto://burrjaw@earthlink.net
         -- http://home.earthlink.net/~burrjaw
         -- Seattle N47.4723 W122.3662 (WGS84) 

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