Canon's compact 20mm ultra-wide prime with USM — lightweight full-frame coverage at f/2.8.
The Canon EF 20mm f/2.8 USM launched in 1992 as a compact ultra-wide prime for the EF mount system. It provided 20mm ultra-wide coverage with ring-type USM autofocus in a remarkably small and lightweight package that remained in production for decades.
Optically adequate — sharp in the centre from f/5.6 with moderate corner softness on full-frame. The USM motor provides fast, silent AF with full-time manual override. Some barrel distortion at 20mm is expected. Basic optical design with limited coatings by modern standards.
Canon EF mount with 72mm filter thread. Approximately 405g. No image stabilisation. Full-frame coverage. Minimum focus distance 25cm — useful for environmental close-ups. Simple rear-focus design. No weather sealing.
Available used at budget to mid-range prices. The Sigma 20mm f/1.4 Art is dramatically better. Canon never made an L-series 20mm prime — the RF 16mm f/2.8 STM serves the ultra-wide role on mirrorless. Adequate as a budget ultra-wide for Canon EF bodies. Check for smooth USM operation.