Canon FD 35mm f/2 S.S.C.

Some copies of this lens are slightly yellow. Hold one up to a white wall and you can see it. That is thoriated glass, the radioactive high-index stuff Canon used in a handful of S.S.C. lenses in the early seventies, and the tint warms your color film by a hair. The radioactive copies are the early concave-front-element S.S.C. version, and that front element is the most reliable visual tell collectors look for: both front and rear use thoriated glass, with the rear element the hotter emitter of the two. The yellowing is not permanent. Days to weeks of strong UV will largely clear it, though a copy stored in a dark closet can yellow again. It is harmless at shooting distance, and it is the single most distinctive thing about the early FD 35mm f/2. People hunt these down specifically for what that glass does to the rendering.

Wide open at f/2 the corners go soft and contrast drops, and faces pick up a gentle glow that no test chart will ever forgive. Use it on purpose. Stop down to f/4 and the frame snaps into focus across most of it; by f/5.6 to f/8 it is sharp enough for landscape work and holds contrast well into the corners. The S.S.C. multicoating (Super Spectra Coating, Canon's answer to the flare problem) keeps backlit scenes usable, though shoot straight into a streetlight at night and you will still pull a warm veil and the occasional aperture-shaped ghost. The out-of-focus background stays smooth in the center and gets a little restless toward the edges. It draws the background rather than melting it.

This is a retrofocus wide, the only way to clear the mirror box on an SLR at 35mm. The penalty is some barrel distortion and a little field curvature you will catch on brick walls and never notice on a street corner. The reward is a focal length that lives on the camera as a documentary and travel lens. A 35mm frames close to what you already see, with more room than a 50mm and less of the stretched, leaning look a 28mm gives you.

Who shoots it: people building cheap FD kits on an old AE-1 or A-1, and the mirrorless adapter crowd after the warm, slightly imperfect rendering that newer glass corrects away. The thorium versions in particular get cross-shopped against the SMC Takumar 35mm f/2, the other classic radioactive wide of the era, by anyone chasing that high-index signature. The honest weakness is sample-to-sample consistency. These are fifty-year-old lenses; the early ones can be hazy or carry hardened helicoid grease, and the yellow tint is real if your copy has been kept in the dark.

For the f/2 itself: that extra stop earns its keep in a dim bar or a dusk street, and the 55mm filter thread is the standard one for the era, so screw-on ND and grads are easy to source. When you meter wide open in low light, let Zone Light Meter read the scene at f/2 and place your shadows on the zone you actually want, because that soft, open aperture is where this lens has a personality worth metering for rather than stopping away.