Olympus Zuiko Auto-T 85mm f/2

Pull this one out of an OM-2 bag and the first thing you notice is how small it is. An 85mm f/2 that weighs barely more than a fast fifty, with the same 49mm filter thread as most of the OM line, so it shares caps and filters with the standard Zuikos like the 50mm f/1.8. Olympus built the whole OM system around the idea that pro gear did not have to be heavy, and the 85 is one of the clearest examples. Portrait shooters keep it for what happens at the focus plane, and it earns the spot.

Wide open at f/2 it is already sharp where you put it, which surprises people coming from the era's cheaper short teles. Center detail holds up at maximum aperture; the corners tidy by f/4 and it is fully resolved by f/5.6. The look is what people stay for. Out-of-focus backgrounds go soft and rounded without the nervous edges or onion-ring texture you get from some fast glass, and the falloff from sharp to blur is gradual rather than abrupt. Contrast runs on the higher side, true to Zuiko character whether you have a single-coated or later multi-coated sample, and color leans neutral to warm in a way that flatters skin.

The 85mm length is the reason it lives in portrait bags. It compresses features just enough, lets you stand at a comfortable distance, and the f/2 speed means you can shoot available light indoors and still throw a background well out of focus. It suits low-light, no-flash situations where you want to isolate one face in a crowd. Stopped to f/5.6 or f/8 it doubles as a tidy landscape detail lens, though that is not why anyone hunts one down.

The honest weakness is flare. Point it into a hard backlight or a streetlight at night and you can get veiling and the odd ghost, more so on the earlier single-coated examples. A hood helps a lot, and you should treat one as mandatory. The other catch is price. It was never a kit lens, so it is less common than the 50mm f/1.8 and sells for more than its f/2 spec might suggest.

People cross-shop it against the Zuiko 100mm f/2.8, which is smaller and cheaper, and the premium 100mm f/2 if they want more reach with the same speed. The f/2 wins on the look of the background and the shorter working distance; the 100s win on size or price. It also gets compared to the Nikkor and Canon FD 85s of the same years, and it holds its own optically while undercutting most of them on bulk. That compactness, plus the rendering, is the case for it. One metering note. Because you will use it wide open in dim rooms, the OM bodies meter at full aperture and the lens stops down only on release, so set Zone Light Meter for the actual stop you intend to shoot rather than the wide-open viewfinder brightness, and you will keep skin where you want it on the curve.