Nikon's early rangefinder wide-angle — the W-Nikkor 2.5cm f/4 in Leica screw mount.
The W-Nikkor 2.5cm f/4 is a wide-angle rangefinder lens made by Nippon Kogaku (Nikon) in the Leica screw mount during the early 1950s, when Nikon supplied glass for both its own rangefinder bodies and the wider Leica-thread market. Focal lengths were engraved in centimetres, so the 2.5cm marking corresponds to 25mm in modern terms. It sits at the wide end of Nikon's early rangefinder line, alongside the 2.8cm and 3.5cm W-Nikkors.
This is a manual-focus, rangefinder-coupled Leica Thread Mount lens with a focal length of 25mm and a maximum aperture of f/4. The W prefix on the barrel denotes a wide-angle Nikkor. The lens was engraved in cm following Nippon Kogaku practice of the period. Beyond the focal length, aperture and mount, further optical details should be confirmed against the specific serial variant rather than assumed.
At 25mm the lens gives a broad angle of view suited to landscapes, street scenes, interiors and architecture where a wide field is wanted. As an f/4 optic it favours daylight and stopped-down work over low light. On the rangefinder it typically needs an accessory viewfinder, since most bodies of the era did not frame this wide. Its compact size makes it easy to carry for travel.
On the used market these early wide Nikkors turn up less often than the standard 5cm lenses and are sought by collectors of Nikon rangefinder glass. Check the front and rear elements for haze, fungus and internal cleaning marks, inspect the coatings for scratches, and confirm the aperture blades are dry and free of oil. Turn the focus to feel for smooth, even movement without grinding. The screw mount adapts to Leica M with an LTM-to-M ring and to mirrorless bodies with a further adapter.