Olympus Zuiko Auto-T 100mm f/2.8

The thing that sold this lens was not its rendering. It was that you could forget it was in the bag. Under 5cm long and around 230 grams, the 100mm f/2.8 was Yoshihisa Maitani's compact-OM philosophy applied to a short telephoto: a portrait lens that did not announce itself, on a system built to be smaller than every Nikon and Canon SLR of the mid-seventies. Olympus made an f/2 version too, and that lens is the cult object people chase now. This is the one you actually carried.

Optically it is a plain recipe, five elements in five groups, and the E in E.Zuiko on the front ring is literally the element count. Designs this simple usually go soft wide open. This one stays honest. Contrast and resolution are genuinely usable at f/2.8 across most of the frame, the corners clean up well by f/5.6, and the lens behaves nicely on modern sensors when adapted. Distortion is essentially nil. Lateral color is well controlled. The bokeh at f/2.8 is smooth and unfussy, no nervous edges, no soap-bubble outlining.

Who reached for it: portrait shooters who wanted 100mm working distance without lugging a fast tele, and OM users doing tight documentary and candid work where a discreet kit mattered more than a stop of speed. It is a classic head-and-shoulders length on 35mm. Focus falloff is gentle rather than dramatic, which is the right behavior for faces.

The honest weakness is the f/2.8 aperture itself. The OM 100mm f/2 and the 85mm f/2 both buy you subject separation and low-light reach this lens cannot match, and they are what people cross-shop against when they want the Zuiko look with more glow. There is also mild vignetting wide open, gone by f/4, and the minimum focus distance of about a meter is long enough that you are not doing tight detail work without an extension tube.

Today it sits in the affordable end of the OM lineup, which is the whole appeal. The f/2 sibling commands several times the price for one extra stop, while this one delivers most of the sharpness for a fraction of the money, which is why it stays a quiet favorite among people adapting Zuiko glass to mirrorless. Shooting it wide open for available-light portraits, meter for the face and let the shadows fall. In harsh light the 49mm front thread takes a standard ND or grad, and Zone Light Meter will hold your placement on the subject's skin while you stop down a filter's worth.