"The Tokina AT-X 14-20mm PRO DX is a wide-angle zoom lens with super-fast f/2.0 aperture. This is the fastest lens ever made by Tokina. The lens is designed for use with Nikon DSLR cameras with APS-C (DX) sensors. Super-wide 14-20mm lens for cameras with APS-C sensors Extremely fast F/2.0 constant aperture 3 Aspherical lens elements to for superior sharpness and contrast 4 Super-low Dispersion glass elements to control chromatic aberrations Fast, Quiet Auto Focus Common 82mm filter thread of use with circular PLs and other filters. 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 an all-new 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 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 an|Fast F2.0 Zoom lens|Includes aspherical lens element|Compact Lens|One-touch Focus Clutch Mechanism allows the photographer to switch between AF/MF simply by sliding the focus ring, forward for AF and back toward the camera for MF."