Re: [ATM] Constraints on design

["vladimir sacek" <vlad@copper.net>]

Richard F.L.R. Snashall" wrote:


> 
> Surprisingly, if I use the focal surface set up by ZEMAX or OSLO,
> the difference seems to disappear.  Perhaps ATMOS comes up with
> the wrong solution -- the difference can be several microns.
> 

This is probably due to ATMOS being not looking 
for the best focus, but staying fixated at the nominal paraxial instead.
For instance, any conical concave mirror is evaluated
at its paraxial focus, thus giving four times larger RMS 
wavefront error than what it is at best focus. One either 
has to correct for it by defocusing, or change the 
parameters until best and paraxial foci nearly coincide.

ATMOS also has an issue with coma, in regard to both
wavefront error and Strehl, which get grossly inflated/reduced 
vs. an actual value. That may have been
fixed recently, but I haven't heard of it.

Vlad



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