Nice to see these old lenses being used. Apparently the early rangefinder lenses were very heavy due to the use of brass. Later on more aluminium was used the the lenses became lighter, so I would expect to see a lot of changes internally between early and late examples.
The production of this lens is very strange. Serial numbers start at 50060101, I believe 5006 means June 1950, although the lens did not hit the market until early 1951. They are marked "MADE IN OCCUPIED JAPAN" (MIOJ), and "Nippon Kogaku Tokyo" on the front ring. After a short production run the next batch has different serial numbers starting 253xxx. Somewhere around 256xxx MIOJ is no longer marked on the barrel and the front ring is engraved "Nippon Kokagu Japan". Somewhere around 257xxx the min aperture changes from f16 to f32. Serial numbers for the chrome lens continue up to at least 257430.
Then we have another chrome series with serial numbers from at least 253201 - 265556. These lenses look the same but can be distinguished by name-ring inside the filter which is narrower, has smaller, neater lettering and two holes 180° apart so they can be unscrewed using a spanner wrench. Construction is also a little lighter. Notice the serial numbers completely overlap the earlier series, in fact starting a little earlier and finishing later. Very early ones are never marked Tokyo like the older series with similar serial numbers. I have never found duplicates of the early and late types, the new serial numbers in fact are randomly distributed through the earlier series, so it appears the original series had many gaps which were faithfully recorded, and later filled with the later series! Why would they do this? I've never seen anything like it on any other lens.
By the time the black versions appear, the serial numbers settle down into a more logical sequence
The optics of the rangefinder lens were transferred directly to the F-mount version and remained in production until mid 1969 when the newer Nikkor-Q 135/3.5 was released.
