Hi all I was searching the web to clarify a conceptual issue regarding the wavefront map in Zemax optical design software. Wavefront map in Zemax is suppose to tell us about the aberrations in the optical system. If I propagate a plane parallel beam in air from the object (at infinity) to Image plane without any optical element in between, then I would expect the wavefront error to be zero at the image plane. But that is not so. For some strange reason, the wavefront aberrations become finite on the image plane. Please see the screen capture attached with this posting. Anywhere between the object and image plane ( e.g. the dummy surface shown in figure) the wavefront error remain zero. I am missing something very trivial here, which is driving me crazy. Could any of you please shed some light on this? Looking forward to hearing from you.