Modeling wavefront aberration and PSF when imaging through a lenslet array is tricky, because multiple images are formed. In the attached file (which can be downloaded from the link at the end of this article) a 7 x 7 array of lenses forms a grid of spots on the image plane:



While all the geometric functions work well, the FFT and Huygens PSF struggle with systems like this, because wavefront error is measured relative to a single reference sphere, located in the exit pupil of the system. But what is 'the' exit pupil pupil of a system that forms 49 spatially separate images for each object point? Clearly there is no single reference sphere that can be applied, as the wavefront does not converge towards a single image location. OPD plots, wavefront error, PSF (and even the concept of a 'point-spread' function) have no meaning in such a system.

Physical Optics treats the wavefront as a single complex amplitude array, and can therefore treat the case where the beam interacts with a lenslet array more naturally. There are some setup considerations to be made, but otherwise analysis with Physical Optics is straightforward.