Pentax's fast A-series telephoto — a manual-focus 135mm f/1.8 with an 'A' aperture setting.
The SMC Pentax-A 135mm f/1.8 is a very fast telephoto prime for the Pentax K bayonet mount, from the A-series generation with the 'A' aperture position for exposure automation. At f/1.8 it was one of the brightest 135mm lenses Pentax produced for the K mount.
This is a manual-focus lens with a 135mm focal length and a bright maximum aperture of f/1.8, carrying Super Multi Coating and an 'A' setting for camera-controlled aperture. As a fast telephoto it is a substantial lens; confirm element count and filter thread on the specific sample.
The 135mm reach combined with an f/1.8 aperture gives a very shallow depth of field and strong subject isolation, well suited to portraits, available-light telephoto work and indoor sport. The wide aperture also brightens the viewfinder for easier manual focusing.
This fast A-series telephoto is uncommon and sought after, so clean examples command strong prices. Check for haze, fungus and coating wear, confirm the aperture blades are dry and the 'A' position locks, and test focus-ring precision given the shallow depth of field. It fits Pentax K digital bodies and adapts to mirrorless.