Constraints on passive spatial coherence filtering of imaging systems due to properties of the impulse response

Properties of the amplitude and intensity impulse responses of passive optical imaging systems have consequences for the spatial coherence filtering properties of such systems. It is shown that imaging systems that have both space-invariant impulse responses and truncating pupil functions have no capability to block spatially coherent sources while imaging those that are incoherent. However, examples of systems with space-variant impulse responses with approximately such capabilities appear to be realizable for a certain range of parameters. However, even space-variant systems cannot block unresolved coherent sources while retaining the capability of imaging those that are spacially incoherent for the same range of source-plane coordinates.