Pentax SMC Pentax-M 50mm f/1.7

Stop this one down to f/4 and the center goes properly bitey, the kind of sharp where you can count eyelashes, while the corners stay just soft enough that nobody complains. That is the fingerprint of the SMC Pentax-M 50mm f/1.7: a lens that is honest about being a fast fifty rather than pretending to be a clinical macro. Wide open at f/1.7 there is a slight veiling softness, a gentle drop in contrast that lifts the shadows a touch, then it snaps into shape by f/2.8 and is essentially flawless by f/5.6.

The optical block is a six-element double-Gauss, the standard recipe for a normal lens of this speed and era. What sets the Pentax apart is the coating. SMC stands for Super Multi Coating, and Pentax was genuinely ahead of the pack on this in the 1970s. Shoot it into a streetlight or a low winter sun and the flare stays controlled, contrast holds, and you do not get the milky wash that plagues a lot of single-coated normals from the same decade. The rendering is neutral and slightly warm, with bokeh that is smooth in the center of the frame and develops mild cat-eye stretching toward the edges wide open. Not swirly, not nervous, just tidy.

This was the kit lens bolted to a million Pentax ME and MX bodies between 1977 and 1984, which is exactly why it is everywhere and cheap. The M-series was Pentax's compact-camera moment, and the lens follows suit: it is tiny, light, and the focus throw is short and well damped. People who shoot it now are not chasing a look. They want a sharp, small, reliable fifty for a K-mount body or an adapted mirrorless setup, and this delivers that for the price of a sandwich.

The honest weakness is that very widest setting. At f/1.7 the veiling glow means you trade a little crispness for speed, so it is not at its punchiest exactly where you most want the light. Stop down a third of a stop and it cleans up fast. The lens people cross-shop against is the faster SMC Pentax-M 50mm f/1.4, and the surprise for newcomers is that the f/1.7 generally matches or even betters it on resolution, often wide open too. The f/1.4 buys you about half a stop of speed and a contrastier but glowier signature at full aperture, for a good deal more money. Unless you genuinely need that last sliver of light or like the f/1.4's rendering, the f/1.7 is the smarter buy.

It takes a 49mm filter, the common Pentax-M thread, so screw-in ND or a polarizer is cheap and easy to source. One metering note: on open-aperture bodies like the ME and MX the finder stays bright at maximum aperture until the shutter fires, so meter at the aperture you actually intend to shoot and let Zone Light Meter hold it while you read the scene. In dim conditions metering wide open keeps the sensor or finder brightest for accurate composition, then you transfer the reading. No leaf shutter here and no close-focus bellows to correct for, so the metering stays straightforward. Buy it, stop it down a hair, forget about it.