This is a Sonnar formula lens, first introduced in 1952. It was produced in Nikon S-Mount, Contax RF Mount, Leica Thread Mount, and Nikon F-Mount. In 1973 or so, the Nikkor 105/2.5 changed to a Planar formula, supposedly a little bit sharper. This 1952 lens is known for it's out-of-focus...
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