The Canon 20mm f/2.8 USM is a moderately fast wide-angle prime designed for Canon EF-mount DSLRs. Key features include:

Wide Angle. Produces a diagonal angle of view of 94° on full-frame DSLRs, making it a great choice for landscape photography.

Moderately Fast Aperture. While it’s not going to enable pitch-dark shooting, you’ll be able to shoot under-average indoor lighting conditions.

USM Focus Motor. Offers fast, quiet performance with a high degree of accuracy. Its close focus distance of 9.8" enables interesting perspectives at extremely close distances, and the rear-focusing system means no barrel extension or rotation.