Here is my very simple setup
and its spot diagram, which is smaller that Airy Radius, so I wanted to investigate PSF further using FFT PSF
but I don’t get any image, just black window
After that, Zemax is slowing down, stopped work and closed. When open Zemax again, I am getting this message
I have tried with other file ( but with similar simulations) it is happening again - I am getting black screen for FFT PSF and Zemax is down. I am sure my laptop has enough RAMs to accommodate Zemax.