The Tokina AT-X 11-20mm f/2.8 Pro DX with Canon EF mount is an ultra-wide zoom lens Featuring an expanded zoom range and improved optical performance. Designed For use with Canon and Nikon DSLR cameras with APS-C (DX) sensors. Tokina adds to its family of Fast-aperture wide-angle zooms focused on providing photographers professional quality optics and construction at an affordable price. The Fast f/2.8 aperture lens offers an equivalent 16.5-30Mm zoom range. The proprietary optical design uses three aspherical lens elements (2 all-glass molded and 1 P-MO hybrid) to achieve superior contrast, sharpness, and correct for spherical aberrations. Additionally, Tokina uses three SD (super-low Dispersion, "Fk01" And Fk03") glass elements to control chromatic aberrations. This compact Ultra wide-angle zoom lens has a bright, constant f/2.8 aperture making viewing and auto focus possible in low light situations But still maintaining portable size and weight. Tokinas exclusive one-touch Focus Clutch Mechanism allows the photographer to switch between AF and MF simply by snapping the focus ring forward for AF and back toward the lens mount for manual focusing.