There was hope that I would find my Nippon Kogaku K. K. reference books, but that has not happened yet with the other activities here. All that I can remember right now is that the Letter "U" was their designation for Eleven (11) Glass Elements in the lens design, but I cannot recall right now the significance of the Letter "D." This was a fairly early Retro-Focus Design NIKKOR lens.
I bought a 20mm NIKKOR in '71 while an Army still photographer. Still using my favoritest lens!
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