Olympus G.Zuiko Auto-S 55mm f/1.2

This is the lens people buy when they want the OM system to focus in the dark. At f/1.2 the 55mm G.Zuiko gathers more light than almost anything Olympus made for the early OM-1, and that single number is why it still trades for real money fifty years on. The "Auto-S" tag is just Olympus speak for an automatic-diaphragm standard lens, but on the street the only spec that matters is that maximum aperture.

Wide open it trades resolution for atmosphere. There is veiling glow and a touch of spherical aberration at f/1.2 that softens highlights and wraps skin in a low-contrast bloom; backgrounds melt into smooth out-of-focus circles, and in busy foliage the rendering can swirl toward the edges of the frame. Stop down to f/2 and most of the haze is gone. By f/4 to f/5.6 it is genuinely sharp across the frame with contrast you can rely on, which is the gap between this and the cheaper 50mm f/1.8 Zuiko: the f/1.8 is sharper sooner, but it cannot do what this does at full bore.

The optical layout is seven elements in six groups, the kind of fast standard-lens double-Gauss family Olympus pushed harder still in the later 50mm f/1.2 OM-System Zuiko that succeeded it. Owners cross-shop those two constantly, and the honest summary is that the newer 50/1.2 cleans up the wide-open softness while this 55mm keeps more of the vintage softness people went looking for in the first place. Flare control is only fair, since an old single-layer coating against a bright window will throw veiling glare, so a deep hood is worth keeping on the front.

A note on color. The early single-coated 55/1.2 uses thoriated (radioactive) glass, and many surviving copies show a warm or yellow cast where that front element has yellowed with age. It is not purely the lens's native rendering; on a badly yellowed sample the shift can be partly reversed with sustained UV exposure. Worth checking a copy against a grey card before you blame the optics.

This is a portrait and available-light lens first. Window light indoors, bars after dark, subject separation on a 35mm body without carrying an 85mm. It is not a landscape lens you reach for first, and it is not one you stop down to f/16 expecting miracles; diffraction and the modest minimum aperture mean the sweet spot is the middle of the range. The build is the usual OM mix of metal and glass, compact and surprisingly light for an f/1.2, with a focus throw long enough for precise work up close.

The honest weakness is the wide-open performance itself. If you need critical sharpness and clean highlights at f/1.2, this lens will fight you until you close it down a stop, and the big front element makes it flare-prone into the light.

One field note. Metering at f/1.2 in a dim room is exactly where a fast prime pays off, but the meter still has to keep up. When you are working in that bottom rung of light, set Zone Light Meter to your actual taking aperture and let it place the shadows, because at f/1.2 a half-stop error is the difference between a usable frame and mud. The 55mm filter thread takes standard rings if you want to add an ND for shooting wide open in daylight.