Pentax's compact M-series short tele — a manual-focus 100mm f/2.8 with Super Multi Coating.
The SMC Pentax-M 100mm f/2.8 is a compact short-telephoto prime for the Pentax K bayonet mount, from the M-series generation built to be small and light alongside Pentax's downsized bodies. The 100mm sat just above the classic portrait focal lengths.
This is a manual-focus lens with a 100mm focal length and a maximum aperture of f/2.8, carrying Pentax's Super Multi Coating. The M line prioritised compactness, so the barrel is short for the focal length; confirm the filter thread and other details on the specific sample.
At 100mm the short-telephoto reach flatters portraits and helps isolate subjects, and the f/2.8 aperture gives a shallow depth of field with smooth background rendering. It also suits tighter general shooting and details from a working distance.
Compact M-series short telephotos are affordable and easy to adapt, making them popular with users of vintage glass. Check for haze, fungus and coating marks, confirm the aperture blades are dry and quick, and test the focus ring for smooth movement. It fits Pentax K digital bodies and adapts to mirrorless.