Ray and van Cittert-Zernike characterization of spatial coherence

We discuss a ray and a van Cittert-Zernike characterization of spatial cohe rence 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 o f the illuminated object and a ray-tracing methodology with which to determ ine this modulus. For uniform illumination of the pupil we relate the modul us 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. (C) 2001 Opt ical Society of America OCIS codes: 080.3620, 110.3960, 110.4980.