Pentax's acclaimed 100mm macro prime, a sharp and affordable choice for K-mount shooters.
The Pentax SMC FA 100mm f/2.8 Macro is Pentax's standard macro prime for K-mount bodies, providing a 100mm telephoto perspective with true 1:1 (1.0x) reproduction ratio at close focus. The FA designation marks it as a film-era full-frame K-mount design fully compatible with digital Pentax K-mount bodies — the lens covers the full-frame K-1 sensor as well as APS-C K-3 and K-70 bodies. A later D-FA version added weather sealing and updated coatings while maintaining the same 100mm f/2.8 Macro specification.
The optical design uses 9 elements in 8 groups. Eight aperture blades produce smooth out-of-focus rendering for the portrait and macro use case. The 49mm filter thread is notably compact for a 100mm macro prime, consistent with Pentax K-mount's compact design tradition. At approximately 340g the lens is light for a macro prime. Minimum focus distance of approximately 0.305m achieves 1:1 (1.0x) reproduction — life-size on the sensor. There is no optical image stabilisation; in-body Shake Reduction (SR) on compatible Pentax bodies provides stabilisation, including at macro working distances.
The FA 100mm f/2.8's dual role covers portrait photography and true macro work from a single lens. For portraiture the 100mm perspective provides natural facial compression on full-frame and APS-C K-mount bodies. For macro photography 1:1 reproduction at the 0.305m minimum distance provides comfortable working clearance from the subject — more than 50-60mm macro lenses at equivalent magnification, leaving room to position lighting or avoid disturbing small subjects. The f/2.8 aperture enables selective focus for both portrait background separation and macro subject isolation.
On the used market the Pentax FA 100mm f/2.8 Macro is affordable and available within the Pentax K-mount ecosystem. Condition checks: AF motor response across the full macro-to-infinity range, front element for cleaning marks, and focus ring smoothness. No weather sealing — the D-FA version with weather resistance is the upgrade for outdoor macro work. Compatible with Pentax K-mount digital bodies including the K-1 full-frame, K-3 III APS-C, and entry K-mount bodies. Adapter use on other brands' mirrorless bodies is possible; confirm AF compatibility for the target system.