[ATM] additional lurie-houghton degrees of freedom

[vladimir sacek]

Richard,

> vs> Using "aplantic" radii, and all else equal, for Guy's system,
> vs> only with the mirror radius changed to R=-80" (-2000mm), 
> vs> results in spherical aberration...
> 
> 80" differs from 2000mm by over 1%. You can't just throw away
> digits with this stuff, it can cause big errors.

I'm just being consistent in equating 80" with 2000mm ;)
Sorry about it. But there is no big errors. Put a corrector 
optimized for R=-2032mm sphere against one with R=-2000mm  
(I better stick with millimeters) and the result is slight spherical 
and coma induced, astigmatism slightly reduced, and the field 
curvature reduced by nearly a factor of 2.5. The chromatism is 
nearly unchanged. Which one you'd rather have?

Vlad