Komura 105mm f/2.8

Sankyo Koki’s Komura 105mm f/2.8 is the lens the reference literature forgot: it appears nowhere on camera-wiki’s Nikon rangefinder page, and its existence in the S mount rests entirely on collector evidence — a Rangefinderforum thread documenting a physical example with photographs and a period brochure, and a first-hand Japanese account of the Komura lineup. That account places it among the initial four lenses Sankyo Koki offered for the Nikon mount, alongside the 35mm f/2.8, 80mm f/1.8, and 135mm f/3.5, and in period it sold as the affordable alternative to Nippon Kogaku’s own Nikkor-P·C 10.5cm f/2.5.

Sankyo Koki (三協光機) was founded in 1951 and adopted the Komura brand name in 1955, building a business on third-party lenses before ceasing operations in 1980. Its S-mount line ran from the late 1950s into the early 1960s and followed the same convention as Tanaka Kogaku’s Tanar lenses: an “N” marked on the barrel to distinguish Nikon-mount examples from their Contax counterparts — though some examples carry no mount marking at all, possibly production from after the Contax versions were dropped. For the 105mm f/2.8, the Leica-screw version is the one the record dates: introduced in 1958 and discontinued in 1964, when the 105mm f/2.5 replaced it, per Japanese Wikipedia citing Classic Camera Senka No.50. No document dates the S-mount version specifically, but its membership in the initial four points to the same late-1950s window.

Sankyo Koki’s own brochure page for the lens survives, and it settles most of what the reference books never recorded. Five elements in four groups, sixteen blades behind a 48mm screw-in filter, click stops from f/2.8 to f/22, five feet to infinity, a 23-degree angle of view, and a viewfinder and leather case in the box. The click stops are worth dwelling on, because the brochure names them as a rangefinder feature — the later SLR-mount Komura 105s use a preset ring instead, so the aperture action alone separates an RF lens from its SLR namesake on a dealer’s shelf. The printed optical diagram also narrows the one question that had stayed open. It shows a substantial front group and, past a wide air space, two small elements near the rear — the asymmetric layout of an Ernostar derivative rather than the mirrored halves a Planar would show. That matches how most sources describe Komura’s fast telephotos, and sits awkwardly with the one collector reading that called the diagram Planar-like.

What the brochure does not give is a number. Sankyo Koki published no production figures, no S-mount price list survives, and no dedicated review of the rangefinder-era lens in either mount has yet surfaced. For a lens that sold as the budget answer to one of Nikon’s best-loved telephotos, it remains one of the quieter mysteries of the system — though it is no longer quite the blank it was: a photographed example, serial 4340244, carries no N or C marking anywhere, which is exactly what you would expect of late production made after the Contax versions were dropped. A second Nikon-mount example, 4345339, carries a smaller but more portable fact on its face: the bezel reads f=105mm over Sankyo Kōki Japan, where 4340244 reads 105mm over Sankyo Kōki Tokyo. The same two styles, in the same order, appear on the 135mm f/3.5 — early lenses giving the bare focal length and Tokyo, later ones the f= prefix and Japan. No published source consulted records that records this, and offer it as an observation rather than a citation: it emerged from laying photographed examples side by side while building this catalogue. If it holds across the rest of the line, a Komura can be roughly dated from its bezel alone, without any serial table — and on this lens it puts the changeover between those two numbers. It rests on a handful of lenses, so more examples could sharpen it, or break it.