Pentax SMC Pentax-K 50mm f/1.4

In 1975 Pentax tore up its own playbook. The company had built its reputation on the M42 screw mount, the Spotmatic, the Super-Takumar glass that screwed in and out by hand. Then it dumped all of it for a bayonet. The new K mount needed a flagship standard lens on day one, and this is what shipped: the SMC Pentax-K 50mm f/1.4, the direct bayonet-mount heir to the SMC Takumar 50mm f/1.4 that screw-mount shooters had loved for years. Same basic seven-element double-Gauss recipe, new mount, the same Super-Multi-Coating that the SMC initials stand for.

That coating is the part people underrate. In the mid-seventies most fast fifties still flared into milk against a backlight. Pentax was multi-coating every air-to-glass surface when a lot of rivals were not, so this lens holds contrast into the sun better than its age suggests. Stop down past f/4 and you get a flare-resistant, high-microcontrast standard lens that is genuinely sharp across the frame.

Wide open is a different animal, and that is the point of buying an f/1.4. At maximum aperture there is a soft glow on highlights and a touch of spherical aberration that some people chase on purpose. Out-of-focus backgrounds go smooth and rounded rather than nervous, with none of the harsh double-line edges that plague cheaper designs. Skin at f/1.4 to f/2 looks flattering in a way clinical modern glass does not bother with. By f/2.8 the glow is gone and it sharpens up fast.

Plenty of people still reach for it. Shooters on Pentax bodies, the LX or the MX or any of the millions of K-mount cameras, plus the mirrorless crowd who adapt it for a cheap, characterful nifty fifty with real metal in the barrel. It cross-shops against the Canon FD 50mm f/1.4 and the Nikkor 50mm f/1.4 of the same era, and it holds its own against both. The K version specifically is the chunky early one, all metal and a proper focus throw, before Pentax slimmed the line down into the M series.

Now the weakness, which is the same one every f/1.4 double-Gauss carries. Wide open in the corners it is soft, and there is field curvature, so flat subjects at f/1.4 will not be crisp edge to edge. If you need corner sharpness, you stop down or you buy a slower fifty that was optimized for it. Worth knowing too: the focus ring on well-used copies often needs a relube, since fifty-year-old grease stiffens.

One metering note. The whole reason you bought an f/1.4 is shooting in light where slower glass gives up, so meter at the working aperture in Zone Light Meter and let it place your shadows before you open all the way up. The 52mm front thread is the standard Pentax size of the period, so screw-in filters swap straight across the rest of your kit.