Investigations have been carried out on the combined effects of amplitude and phase variations in a periodic complex object on the image formed in a partially coherent optical system in the presence of defocusing. To examine these effects, images of one-dimensional periodic complex objects and the two-dimensional Siemens Star are simulated with various different complex transmittances. A number of significant phenomena are clarified through observation of the simulated images and evaluation of the image contrast for the fundamental and second harmonic spatial frequency components. One of the results is that object phase variations are extremely important to the image appearance in the defocused system and to the change of contrast reversal frequency with defocusing under incoherent and partially coherent illumination, but not in the coherent case.
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