Pentax's A-series short-tele macro — a manual-focus 100mm f/2.8 with close focus and an 'A' setting.
The SMC Pentax-A Macro 100mm f/2.8 is a short-telephoto macro prime for the Pentax K bayonet mount, from the A-series generation with the 'A' aperture position for exposure automation. The 100mm macro gave more working distance than the 50mm macro for close-up work.
This is a manual-focus lens with a 100mm focal length and a maximum aperture of f/2.8, carrying Super Multi Coating and an 'A' setting for camera-controlled aperture. It focuses much closer than a standard 100mm; verify the exact maximum reproduction ratio and filter thread on the specific sample.
The 100mm macro doubles as a sharp short-telephoto portrait lens, while its close focus and greater working distance suit insects, flowers and small objects that a 50mm macro would crowd. The longer focal length eases lighting at high magnification.
A-series macro telephotos are prized for sharpness and their extra working distance, and clean copies hold their value. Check the focus helicoid for smooth extension, inspect for haze and fungus, confirm the aperture is dry and the 'A' position locks, and test for focus-ring slack. It fits Pentax K digital bodies and adapts to mirrorless.