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But I could swear the concentric circles look like badly polished aspherical surfaces.
Concentric circles can remind us of many things in the world of optics and image processing, where several quantities are a function of the distance from the image center. Aspherical surfaces are an unlikely cause in this case, because each point in the sky receives its light from a large part of the total lens surface, at large apertures anyways. This is different from the blur patches of out-of-focus highlights, where subareas of the blur disks are associated with subareas of the elements. Hence the phenomenon of onion-ring bokeh. You may have a case though if the effect only occurs at small apertures, because the ray pencils contributing to different parts of the sky then traverse different, and relatively small subareas of the lens elements.