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.

Optically it is five elements in four groups, with sixteen aperture blades behind a 48mm filter thread — a specification confirmed twice over, by a period brochure diagram matched against a surviving example and by the 1963 Komura lens guide. What to call the design is less settled: it is usually described as an Ernostar type, like most of Komura’s fast telephotos, but the brochure diagram has also been read as closer to a Planar, and the classification is best left open. Beyond that, the documentation simply runs out: 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.