Pentax's A-series fast fifty with auto-aperture — the preferred version of the SMC 50mm f/1.7 for digital use.
The Pentax SMC Pentax-A 50mm f/1.7 was introduced in 1983 as part of Pentax's A-series lens lineup. It shares the same optical formula as the earlier M-series 50mm f/1.7 but adds the critical A-position on the aperture ring, enabling program and shutter-priority auto exposure on compatible Pentax bodies — making it the preferred version for digital Pentax DSLR use.
Optically identical to the SMC-M 50mm f/1.7, delivering good sharpness from f/1.7 in the centre and excellent results by f/4. The SMC coatings provide effective flare resistance. Bokeh is reasonably smooth with six aperture blades creating hexagonal highlights in out-of-focus areas. A well-proven optical design that delivers reliable results.
Pentax K mount with A-series auto-aperture coupling. Filter thread is 49mm. Weight is approximately 185 grams — very compact. Build quality is excellent with smooth metal construction. The A-position on the aperture ring allows the camera body to control the aperture electronically, enabling all auto-exposure modes on Pentax DSLRs.
Very common and affordable on the used market. Check for smooth focus ring and clean aperture ring detents — ensure the A-position clicks properly. Preferred over the M-series version specifically because of the auto-aperture support on digital bodies. One of the best budget fast primes available for Pentax K-mount shooters.