Nikon Nikkor 13mm f/5.6 AI

Set the 13mm next to a 16mm fisheye and the whole reason this lens exists snaps into focus. The fisheye sees even wider, a full 180 degrees, but it bows every horizon into a smile and lets the corners curl away. The 13mm holds its roughly 118 degrees with every straight line dead straight, edge to edge, which in 1976 was close to witchcraft for a rectilinear lens this wide on the F mount. Architects and interior shooters wanted that geometry, and almost nobody else could afford to want it.

Nikon never really sold the thing in volume. It was built to order in tiny numbers across its long run, and surviving copies trade for the price of a used car, sometimes several. That rarity is half its modern reputation. The other half is earned. Distortion is so low it looks measured rather than corrected, and field flatness holds across the frame in a way that embarrassed most ultrawides for decades.

Rendering. Wide open at f/5.6 it is already working, with mild corner softness that tightens by f/8 and bites hardest near f/11. Contrast is moderate by current standards, the older coating-era look, so it answers well to a little extra development or a contrast nudge in the scan. Flare is the honest weakness. That enormous front element sits out in the open, there is no hood worth the name, and a sun anywhere near the frame throws veiling haze and the occasional ghost. You compose around the light or you pay for it.

There is no front filter thread because the filters mount at the rear instead. The lens shipped with a small set of interchangeable filters, including yellow, orange and red contrast elements that swap in behind the optics. A clear or neutral element changes nothing for exposure, but the colored contrast filters each carry a real factor. Dial that into Zone Light Meter before you meter a black-and-white scene through the orange element, or your shadows land a stop and a half under where you meant to place them.

Who actually uses it now. Collectors, mostly, plus a handful of working architectural and landscape photographers who got one before the prices went stupid. Cross-shopped against the 14mm and 15mm Nikkors, or a modern Voigtlander ultrawide on an adapter, the 13mm wins on rendering character and pure distortion control and loses on everything practical: weight, maximum aperture, cost, and the plain fact that you can buy a sharper modern wide for a fraction of the money. People still chase it anyway, partly for the files and partly for the badge. Both reasons are legitimate.