Komura 105mm f/2

On Western message boards the Komura 105mm f/2 goes by the nickname “King of Ernostars” — a five-element, four-group telephoto in the lineage Ludwig Bertele laid down in the 1920s, and the fastest 105 ever offered for the Nikon rangefinder, out-speeding Nikon’s own celebrated Nikkor-P·C 10.5cm f/2.5. It arrived around 1960 as a late addition to Komura’s Nikon-mount line, and it is rare enough in S mount that its existence there rests on surviving examples rather than any catalog — anchored by a Japanese collector’s first-hand account of his own Nikon S example.

Sankyo Koki was founded in 1951 and sold lenses under the Komura brand from 1955; the company lasted until 1980. Its Nikon-mount line ran from the late 1950s into the early 1960s, following the same convention as Tanaka’s Tanar lenses: an “N” marking on the barrel identified the Nikon fit, though some late lenses went unmarked. The initial S-mount range consisted of four lenses — a 35mm f/2.8, an 80mm f/1.8, a 105mm f/2.8, and a 135mm f/3.5 — with the 105mm f/2 among a handful of later additions that arrived as the rangefinder era was already winding down.

The lens itself pairs its Ernostar formula with a preset 12-blade aperture, a 58mm filter thread, and a 1.5-metre minimum focus. Japanese literature dates the Leica-screw version to 1960, on sale until 1967, and the known Nikon S example dates to around the same year, weighing in near 440g. In use it behaves like the classic large-aperture Ernostar it is: soft wide open, tightening up between f/2.8 and f/4, with background bokeh that goes distinctly swirly at f/2 — the verdict of the collector whose example confirms the mount.

The paper trail is thin. No production quantities are documented anywhere for Sankyo Koki’s rangefinder lenses, and no S-mount price list survives; the only surviving original price is American — $120 for the Leica-screw version on the 1965 EPOI list. One caution for collectors: the later Komura 105mm f/2.5 shares this lens’s optical design and improves the close focus to 1 metre, but no source places it in S mount — it belongs to the SLR/Unidapter era — so the f/2 stands as the end of the line for the fast Komura 105 on the rangefinder.