Zernike mixing - ??? Hi. I understand that Zernike was a physicist and that he did some work in optics, and am also aware of the Zernike Polynomials which are used in optics to describe aberrations in lenses, etc. What I do not understand is a comment that I got (from a non-native English speaker) in comparing optical materials (Si and Zr) regarding one having "Zernike Mixing" (apparently not desirable) and another not having it. What is "mixing" in "Zernike Mixing"? Does it refer to the mixing of different kinds of aberrations (polynomials) or something akin?