Since we are dealing with Nikkor lenses, and minutiae concerning them, I thought it might interest some here to compare early and late version CRT Nikkors. The early versions have serial numbers starting with 7; later version numbers start with 8. The later version has the magnification marked on the beauty ring (M=1/5). I have one of each, and they are noticeably different in rendering. I suspect that the earlier version is not optimized to 1/5, but for slightly greater distances, based on the higher negative field curvature of the later version. There is also a difference in size of the center subject, probably resulting from the difference in field curvature. Just for fun, here are two comparison shots. You'll notice that the earlier version is slightly warmer in color, slightly longer in focal length (or at least the center subject is slightly larger, and does not have as much field curvature as its later sibling. Obviously this shot is taken at a much longer distance than that for which the lens is optimized, but it's clear that they are not exactly the same.
