Nippon-Kogaku Regno-Nikkor 1:2 f=5cm Nippon-Kogaku Nr.141xxx

This series is generally similar to the 5cm 1:2 with 50xxx serial numbers.However there are a few intersting differences: I am unsure where this lens fits into the scheme of things. The f11 aperture suggests this lens is earlier than the 5cm 1:2 with 50xxx serial numbers - manufacturers tend to add features to a new lens, not remove them. On the other hand the 5cm 1:2 50xxx series is probably contemprary with the 5cm 1:3.5 with the same serial numbers, and they were made before the 5cm 1:3.5 502xxx series which has a similar style name-ring as the Regno.

The "Regno" designation is also used with the Regno-NIKKOR 10cm 1:1.5 Indirect X-Ray Photography Device. It seems unlikely this lens was also intended for X-Ray photography, or was there some other special purpose for this lens, which only required stopping down to f11? The name-ring on the 10.5cm Regno is also a later style, so it appears the 5cm Regno is an earlier lens. Confused? If you have any information about this (or any other early Nikkor) let me know.

The pictures below show a lens with an "A" following the serial number. Is this an early indication of a duplicate serial number? N-K would later use a colon ":" to indicate duplicate serial numbers. The lens below also appears to be missing the black ring around the lens base, revealing bare screw threads.

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