Canon EF 50mm f/1.2L USM

Shoot this lens wide open and the plane of focus drifts back as you stop down. Focus shift is the EF 50mm f/1.2L's signature, baked into a fast double-Gauss design that trades corrected spherical aberration for that glowing, slightly soft look at f/1.2. Nail focus on the eyes at maximum aperture, then close to f/2 for depth, and the sharp zone has crept behind where you metered it. Canon never fully tamed this. Every long-term owner learns to focus-and-recompose around it or live with the dreaminess on purpose.

The glow is why people buy it. At f/1.2 the lens renders skin with a soft halo of low contrast, backgrounds go smooth and creamy, and out-of-focus highlights bloom into big round discs on axis. Toward the edges of the frame those highlights take on the usual cat's-eye shapes you get from any fast fifty wide open, and they round out as you stop down. By f/2 the veil starts lifting; from f/2.8 to f/4 it firms up into a properly crisp portrait lens with rich, saturated Canon color. Flare is reasonably controlled for an f/1.2 lens, helped by Super Spectra coating, though it does not match the newer mirrorless f/1.2 designs that came after it.

It is heavy. Around 580 grams of glass and metal with a 72mm filter thread that dwarfs the 58mm rings on cheaper Canon fifties. Autofocus through the ring-USM motor is quiet and confident in daylight but hunts in dim rooms, the exact low-light situations where you bought an f/1.2 in the first place. That is the honest weakness, paired with the focus shift. You shoot this lens slow and on purpose, not on the run.

Wedding and editorial portrait people are the core users, the ones who want one frame at f/1.2 with the bride's eyes tack sharp and everything else dissolved. It gets cross-shopped against the lighter, cheaper, optically cleaner EF 50mm f/1.4, and against Sigma's 50mm f/1.4 Art, which is sharper wide open but lacks the rendering character. People still pay the L-series premium for the look, not the spec sheet. Over the f/1.8 budget option that extra stop of light buys you roughly a full stop, plus a rendering signature that is hard to reproduce by other means.

For metering, the value of that f/1.2 maximum aperture shows up in available darkness. A church interior or a candlelit reception room that forces ISO 6400 on a slower lens opens up at f/1.2, so meter wide open in Zone Light Meter to see how much shutter speed the extra light actually buys you before you commit to a shooting aperture. Then factor in the focus shift and decide what you want from the frame, because on this lens the maximum-aperture glow and peak resolution do not live in the same shot.