The Tokina AT-X 14-20mm f/2 PRO DX Lens for Canon EF is a wide-angle zoom lens with super-fast f/2.0 aperture. This is the fastest lens ever made by Tokina. Tokina adds its fastest lens to date to its family of fast-aperture wide-angle zooms focused on providing photographers professional quality optics and construction at an affordable price. The extremely fast F/2.0 aperture lens offers an equivalent 21-30mm** zoom range. The super-bright, constant F/2.0 aperture makes viewing, auto focus and shooting possible in very low light situations while still maintaining reasonable size and weight. The 14-20mm F/2.0 has a proprietary optical design that 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 of an four SD (Super-low Dispersion, 'FK01' and FK03') glass elements to control chromatic aberrations. Tokina's 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. The lens is also designed to stand up to the rigors of daily use by photographers in a wide variety of shooting conditions and environments.