We discuss a ray and a van Cittert–Zernike characterization of
spatial coherence in condensers for projection systems. We present
a rule of thumb with which to estimate the modulus of the coherence
function at a given point of the illuminated object and a ray-tracing
methodology with which to determine this modulus. For uniform
illumination of the pupil we relate the modulus of the coherence
function and the pupil-filling factor. We suggest that the rms of
the angular ray spread at a given object point is an appropriate metric
with which to characterize local coherence properties.
© 2001 Optical Society of America
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