Nikon Fisheye-Nikkor 16mm f/2.8 AI-S

Cross-shop it against the Canon FD 15mm f/2.8 and you get two lenses doing the same trick from opposite camps. Both are full-frame diagonal fisheyes, both open to f/2.8, both throw a 180-degree image corner to corner. Which one is "better" usually comes down to which mount you already own, and the arguments people have about corner sharpness and flare tend to be more about copy variation and shooting style than any settled measurement. What is not in dispute is that this Nikkor is a serious working fisheye, not a novelty, and a lot of the bodies it shipped on got sold long before the lens did.

Optically it is a retrofocus design built to clear the F-mount mirror box, which is the whole engineering problem of a fisheye at 16mm. The barrel distortion is the point, not a defect, so judging it like a 16mm rectilinear misses what it is for. A line through the dead center stays straight; everything off-axis bows. Wide open the center is already strong and the extreme corners soften, which is normal for the type. Stop down to f/5.6 or f/8 and the whole field firms up. The earlier Fisheye-Nikkor 16mm f/3.5, the predecessor this one replaced around 1979, covered 170 degrees rather than a full 180, so the f/2.8 buys you the wider diagonal and a faster maximum aperture, not necessarily a sharper center.

Filtering is where people trip up, because there is no front thread and the curved front element will not take a screw-in anything. Nikon handled it with rear bayonet filters that drop into the back of the lens, one at a time. The L37C is effectively part of the optical formula and stays mounted for infinity focus, and the kit came with three more to swap in behind it: the O56 orange, the A2 light amber, and the B2 light blue. If you shoot black and white and want sky contrast, the O56 is the one you reach for. It is a slower system than threading a filter, but on a 180-degree lens it is the only system there is.

Genres it fits: tight interiors and architecture where you need the entire room in one frame, performers shot from the photo pit, action work where the bent horizon is the look, and deep-foreground landscapes with a near rock filling the bottom and the skyline curving across the top. It is not a portrait lens, full stop. The honest catch is flare. With 180 degrees of coverage the sun is in the frame more often than not, and you will fight veiling flare and the odd ghost no matter how careful you are. Plan compositions that keep the sun out of the worst spots, or use it on purpose.

At f/2.8 it gathers enough light to meter and focus by in dim rooms, and Zone Light Meter will hold the wide-open reading while you set exposure. Depth of field is very deep here, so a hyperfocal setting covers most scenes, though wide-open work with a close foreground (this lens focuses down near 0.3m on a floating element) still rewards getting the near subject actually sharp. Used prices stay reasonable, partly because few photographers need a fisheye and partly because Nikon built this one for nearly two decades, so copies are not scarce. Against the later 16mm f/2.8D AF version it gives up autofocus and wins on the manual barrel feel. If a fisheye is what you want in F-mount, this is the one to find first.