function s0 = ComputeDiffLimit(pupil,nm)
% s0 = ComputeDiffLimit(pupil,nm)
%
% Compute the diffraction limit for coherent light.
% (For incoherent light the answer is 2*s0.)
% See page 120 in Goodman.
%
% "pupil" diameter in mm
% "nm" is wavelength in nm
% "s0" is highest spatial frequency passed by the pupil in cycles/deg
%
% Goodman, J. W. (1968) Introduction to Fourier Optics.
% San Francisco: McGraw-Hill. Page 120.
%
% Goodman's formula involves di, which I think is the distance to the
% image. Goodman's formula gives the limit in
% cycles/unit length. The formula below gives
% the answer in cycles/degree.
% 7/11/94 dhb Added this comment.
% 9/8/02 dgp Cosmetic.
s0 = tan(2*pi/360)*pupil/(2*nm*1e-6);