Along with 11 mm starting focal length and 9-blade circular aperture, Canon EF 11-24mm f/4L USM ultra wide-angle zoom lens features wide angle of view (126° 05' diagonal) and optics comprised of 16 elements in 11 groups with 3 group zoom system and rear focus. This rectilinear full-frame Digital SLR lens offers optimized AF algorithms and full-time manual focus capability. Optical design with 4 aspherical lens elements minimizes distortion across entire zoom range.