Overview

The Pentax SMC-FA 20mm f/2.8 is a discontinued full-frame wide-angle lens. Optically, it delivers very good center sharpness from f/2.8, with excellent results at f/5.6-8, but borders are only acceptable wide open. Weaknesses include pronounced barrel distortion (2.5%), strong vignetting at f/2.8 (~1.2EV), and low contrast at f/2.8. Build quality is fine with a smooth focus ring, but plastic quality could be better; it uses a screw-drive AF that is fast but noisy. It suits architectural and outdoor photographers seeking a compact, lightweight travel lens.