A surprisingly large number of papers have been written on the effects of partially coherent light in image formation (for a recent review see Thompson 1969). Thus the major effects that can occur are well documented. With imaging systems that are used with transparent objects the characteristic edge ringing and edge shifting are familiar results. In reflective systems the speckle pattern is usually the most severe effect that often masks the ringing produced by coherent object illumination. Thus this paper will be primarily concerned with systems used in transmission. It is important to note that the majority of papers in this field assume diffraction limited performance of the imaging optics; this is, of course, laudable if the system is to be used with incoherent object illumination. If, however, the system is to be used with coherent or partially coherent object illumination then other considerations become important.