Nikon patent application 20120182617 is for a 300mm f/4 with VR. The interesting part is that the overall length of the lens is relatively short ~ 190mm (around 7.5 in.) with back focus – so real length would be ~150 mm, much shorter than the existing 300/f4 (222.5mm/8.8 in):
Size comparison between the new Nikon patent with diffraction surface and the current 300mm f/4 lens
In the patent calculations one of the surfaces is marked as “Diffraction surface” which is probably the reason for the compact lens size. I believe this is the first full lens patent with diffraction. See also Canon’s explanation of the Diffractive Optical (DO) element.
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