Pentax SMC Pentax-M 50mm f/2 (K)

When Pentax launched the M series in 1976, the brief was size. The ME and MX bodies were among the smallest 35mm SLRs anyone had built, and the old K-series lenses looked clumsy bolted to them. So Pentax shrank the optics to match. The SMC Pentax-M 50mm f/2 is the cheap-seat normal in that lineup, the lens that shipped on used bodies far more often than anyone walked into a shop asking for it. Every system needs a budget fifty, and on a pocket-sized ME a big normal defeats the point.

Optically it is a simplified five-element design, one glass short of the classic double-Gauss used in its faster f/1.7 and f/1.4 siblings. That economization is the whole point of the lens. Wide open at f/2 it is soft in the corners and a touch low in contrast, the way nearly every cheap fast fifty of the era was. Stop down to f/4 and it sharpens up fast. By f/5.6 to f/8 it is genuinely crisp across the frame, and that is where most people who know the lens park it for landscape and travel work. The six-bladed aperture gives bokeh that reads smooth rather than dreamy. Behind a subject the falloff is gentle, never nervous or doubled, but those six straight blades stamp out-of-focus highlights as soft hexagons once you leave f/2, not perfect circles.

The real argument for this lens is the SMC coating. Super-Multi-Coating was Pentax's bread and butter, and even on a budget normal it earns its keep. Shoot into a window or a low sun and flare stays controlled, veiling is minimal, and color comes back neutral with a slight warmth that suits skin. That coating is why a forty-dollar lens can hold its own against glass costing five times as much.

Who shoots it. Students, first-roll film shooters, and anyone building a light K-mount kit that rides on an ME or MX all day. It is a fine portrait lens at f/2.8 and a reliable street fifty stopped down. People cross-shop it against the f/1.7 and f/1.4 versions of the same line, and that comparison is the honest weakness here. The f/1.7 is barely larger, costs about the same used, and gives you about half a stop more light plus the full six-element design and a small edge in wide-open contrast. If you can find the 1.7, most shooters take it. The f/2 survives because it is cheap and absolutely everywhere.

The 49mm filter thread is the same across most of the small M primes, so one set of ND or polarizers covers your whole bag. If you are working in dim interiors at f/2 with the finder going dark, meter the scene in Zone Light Meter and place your shadows by hand rather than trusting a fading TTL needle. The lens has no quirks that fight you on exposure. Give it a stop or two and decent light and it does the rest.