Pentax's fast K-mount telephoto — a manual-focus 135mm f/2.5 with Super Multi Coating.
The SMC Pentax 135mm f/2.5 is a fast telephoto prime for the Pentax K bayonet mount, from the first-generation K-series range. At f/2.5 it was the brighter of Pentax's 135mm options, above the slower f/3.5 versions in the line.
This is a manual-focus lens with a 135mm focal length and a maximum aperture of f/2.5, carrying Pentax's Super Multi Coating. Details such as element count and filter thread should be confirmed against the specific sample rather than assumed across the different 135mm designs.
The 135mm telephoto reach with an f/2.5 aperture suits portraits, tighter details, daylight sport and low-light telephoto work. The relatively fast aperture gives a shallow depth of field and strong subject isolation at this focal length.
Faster 135mm primes hold their value better than the common slower ones, so expect a modest premium for clean glass. Check for haze, fungus and coating marks, confirm the aperture blades are dry, and test the focus ring for smooth, precise action. It fits Pentax K digital bodies and adapts to mirrorless with an adapter.