The Influence of Spatial Coherence on the Monochromatic Optical Transfer Function

It is widespread practice to measure the optical transfer function (OTF) by scanning the images of 'simple' objects. However, the illumination used in such systems is (generally) partially coherent, and not incoherent as is required by theory. The influence of spatial coherence is explicitly examined in order to obtain a general equation for the observed OTF for the case of one-dimensional test objects. The equation is applied to the case of a 'perfect' rotationally symmetric lens, using a slit object, and, on comparing the results with the true (incoherent) OTF of such a lens, significant differences have been found.