Canon EF-S 17-55mm f/2.8 IS USM LensA tremendously flexible standard zoom for APS C format DSLRs, the EF S 17 55mm f 2. 8 IS USM from Canon pairs the 27. 2 88mm equivalent focal length range with a bright f 2. 8 constant maximum aperture. Benefitting this design is a sophisticated optical layout, which includes both Ultra Low Dispersion glass and aspherical elements to significantly reduce chromatic and spherical aberrations for improved clarity and sharpness throughout the zoom range.