Nikon's rare 220-degree circular fisheye — the manual-focus 6mm f/2.8 for the F mount.
The Fisheye-Nikkor 6mm f/2.8 is one of Nikon's rarest optics, a large circular fisheye for the Nikon F system introduced in the early 1970s. It was built to cover a 220-degree field of view, meaning it sees slightly behind its own mounting plane, and it was produced in very small numbers for scientific and specialist use. Its enormous front element and deep body make it instantly recognisable among Nikon lenses.
This is a manual-focus Nikon F lens with a maximum aperture of f/2.8 and a fixed 6mm focal length. It produces a circular image inside the frame and offers a 220-degree angle of view, wider than a hemisphere. It uses built-in filters rather than a front thread. Given its rarity, only the verified focal length, aperture, mount and field of view are stated here; construction details vary across sources and are omitted.
The look is an extreme circular fisheye projection, with the entire visible sphere in front of the camera compressed into a small circle on the film. It suits scientific recording, sky and cloud studies, and any application needing more-than-hemispherical coverage. It is a collector and research instrument rather than a practical photographic tool.
On the used market this lens is exceedingly scarce and sells for very high sums when it appears, almost exclusively to collectors and institutions. Inspect the huge front element for scratches and coating wear, confirm the internal filter mechanism operates, and verify the aperture blades are clean and dry. Its deep rear group and mirror-lock-up requirement make routine use and mirrorless adaptation impractical.