Mamiya Mamiya-Sekor C 80mm f/1.9 N

Mamiya never made a faster lens for the 645 mount than this one. The normal lens everybody owns on a 645 body is the 80mm f/2.8, and it is genuinely good. The f/1.9 is the one people hunt for and pay up to get. On a 6x4.5 negative, f/1.9 carves out a sliver of focus depth that no full-frame 50mm can reach, and that is the whole reason it exists.

Open it up and the highlights take on a gentle veiling, not soft in a broken way but glowing, with a focus plane that is sharp exactly where you put it and falls off fast on either side. Skin looks like skin, pores present, texture forgiving. Stop to f/4 and it tightens across the frame; by f/5.6 it is genuinely crisp corner to corner on medium format, which is a tall order for any fast normal. The out-of-focus rendering is the selling point. Smooth, rounded, no nervous edges, backgrounds that dissolve into color instead of clutter. Point lights near the edges go slightly oval the way fast normals do, but it never turns busy.

Contrast sits moderate, which is right for a portrait lens. It holds shadow detail and does not crush the midtones into a wall. Flare resistance is decent for the era without being bulletproof, so shoot it into a window with no hood and you get a wash of veiling glare. Keep the shade on. This is a late-film-era, double-Gauss derived design, and it carries the warm, slightly classic Mamiya signature rather than the clinical bite of a modern Otus or a Fuji GF prime.

The people who reach for it are portrait and wedding photographers chasing medium-format tonality with real subject isolation, plus available-light documentary shooters who refuse to drag strobes. It is the closest the 645 system gets to a fast-fifty look with a 6x4.5 frame behind it. The honest weakness is the bulk. This is a big, heavy chunk of glass on the front of an already substantial body, and hand-holding it through a long event is a workout. Manual focus wide open is unforgiving too. That thin depth of field punishes a missed eye, and you will miss a few.

Today it trades at a real premium over the f/2.8, partly on scarcity and partly because the speed earns its keep. People cross-shop it against the Pentax 645 75mm f/2.8 and the Contax 645 80mm f/2, though neither gives you f/1.9 in this mount. One metering note. There is no leaf shutter in this lens, so you are leaning entirely on the body's focal-plane shutter with no high-speed flash-sync trick to fall back on. Meter it wide open in the dark with Zone Light Meter, place your subject's skin on the zone you want, and let the f/1.9 do the rest. The 67mm front takes standard filters if you want to pull an ND for shooting wide open in daylight.