Canon FD 35mm f/2 S.S.C. (concave, radioactive)

Available darkness is where this lens earns its keep. A 35mm framing wide enough to work a room, a maximum aperture of f/2 so you can hand-hold a dim bar or a wedding reception lit by string lights, and a front element that glows faintly amber from the thorium baked into the glass. Most 35s of the era stopped at f/2.8 or f/3.5 and left you sunk once the sun went. This one keeps you shooting.

The recessed front group is what people are chasing. Canon ground a deeply concave first element and loaded the glass with thorium oxide, a dopant that pushes the refractive index high while keeping dispersion low, which buys back the spherical and chromatic correction a fast retrofocus wide normally fights. The catch is that thorium is mildly radioactive, and over fifty years of decay it tints the glass yellow. The fix costs nothing. Leave it face-up in a sunny window or under a UV lamp for a few days and the cast clears. Plenty of black-and-white shooters never bother, because that warmth behaves like a built-in yellow filter, dropping skies a touch and flattering skin. The early FD also used floating elements to hold performance at close focus, which was not a given on a wide this fast in 1973.

Rendering is contrast-forward and usable from f/2, the center decently sharp while the corners trail, hitting its stride by f/2.8 to f/4 and tightening fully across the frame around f/5.6 to f/8. Flare behavior is better than the recessed glass has any right to be. The Super Spectra Coating, the S.S.C. stamped on the barrel, holds contrast with the sun sitting right in the frame and gives you small controlled artifacts instead of a washed-out fog. Bokeh is calm and unremarkable rather than swirly, which suits documentary work fine. Geometry is the place it gives ground. Distortion is not heavily corrected, so straight architectural lines bow at the edges, and this is not the wide you reach for to shoot building facades.

People shooting FD bodies still reach for it, as do the mirrorless crowd adapting old glass for a fast normal-wide with a fingerprint. The obvious comparison is the later New FD 35mm f/2, lighter, cheaper, no thorium, and a touch more clinical in its rendering. Buyers who want the softer, warmer signature, or who just like owning a faintly radioactive piece of optical history, pay the premium for the concave version. Prices have crept up as adapter culture found it, but it still lands well under boutique-glass money.

One field note. Wide open in the dark is exactly where this lens wants to live, and it is also where spot metering off a clipped light source will fool you into underexposing the faces you actually care about. Take the Zone Light Meter reading off a midtone, a forehead, a wall, not the bare bulb, and let the f/2 aperture do its job. If you do thread a real yellow or orange filter onto the 55mm front for black and white, dial in the filter compensation so the meter accounts for the light it is eating.