Re: [ATM] Re: Aplantic Gregorian

["Richard F.L.R. Snashall" <rflrs@rcn.com>]

Jim Burrows wrote:

> 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.

I infer you are describing fifth and higher order terms.  Correct?


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