Nikkor-H(·C) 18cm f/2.5

In November 1953 — a date still routinely misprinted as 1955 — Nippon Kogaku answered the celebrated Zeiss 180mm f/2.8 Sonnar with something a third of a stop faster. The Nikkor-H 18cm f/2.5 was a six-element, four-group design of a type the company never named in print, 1.7 kilograms of preset-diaphragm telephoto listing at $400, and it coupled to no rangefinder at all: the lens is a short-mount barrel that focuses and frames only through the Prism Reflex Housing hung between it and the camera, taking Series IX drop-in filters in its reversible 82mm hood and reaching a minimum focus of 2.1 meters. Perhaps 1,200 were made in total, making it one of the rarer prizes of the S-mount system.

The housing’s story is inseparable from the lens’s. Nippon Kogaku patterned its Prism Reflex Housing on the Leitz PLOOT: the Model I, announced in 1952 but apparently not marketed until late 1954, found fewer than 200 buyers, and the improved Model II of around May 1956 — $129.50, serials 471101–471769, so fewer than 800 built — carried 45-degree prism finders (67001–67623) and, late in the run, 90-degree pentaprisms (77001–77056). Every one of the system’s four reflex-housing telephotos lived or died with those numbers, and they explain why the 18cm’s production stayed so small despite its headline speed.

Production breaks into a brief first block of H·C lenses at 373601–373648 with the infinity mark engraved INF., then a jump to the 473xxx series, where the infinity mark becomes oo (473601–473770) and the ·C engraving is subsequently dropped — the plain-H lenses running from 473800 through the final feet/m-scale examples at 474179–474236. The serial spans account for roughly 686 S-mount lenses against Pacific Rim’s estimate of about 1,200 total, and no factory count has surfaced to settle it. Two sibling versions exist: a Leica-thread lens for the Visoflex housing, its examples scattered within the plain-H block rather than given a run of their own, and a Bronica 6×6 version with its own block at 470001–470102 and a closer 1.5-meter minimum focus.

The design outlived its housing. An N-F adapter carried the reflex-housing lenses onto the Nikon F, and by the 1965 price list the same optics were cataloged outright as F-mount preset lenses — the 18cm f/2.5 quietly crossing systems more than a decade after its debut. Its optical formula, though, kept its secret: when Nikon’s own retrospective essay on the 180mm focal length reached for a type name, it applied one — Ernostar — only to the later F-mount 180mm f/2.8, leaving the rangefinder lens’s six-in-four construction unnamed in every source to this day.