Necessary conditions for spatially incoherent illumination of a three-dimensional object

Spatially incoherent imaging systems are characterized by a linear-in-inten sity relationship between the object and the image distributions. While str ict spatial incoherence is theoretically not achievable, a particular imagi ng system may be made effectively linear in intensity by a choice of the ap propriate illumination source location and size. The requirement for source size for effectively incoherent illumination of a two-dimensional object i s well known. I extend the arguments for choosing the source size in a two- dimensional imaging system to develop necessary conditions for the source s ize for effectively spatially incoherent illumination of a three-dimensiona l object. While the conditions are necessary, they are not sufficient, sinc e coherence in the direction of the optical axis is not addressed. (C) 2001 Optical Society of America. OCIS codes: 070.2580, 110.2990, 110.4980, 180. 6900.