The Nikon F-mount Tokina atx-i 11-20mm f/2.8 CF is an ultra-wide zoom that is ideal for landscape, architecture, interior, and astrophotography applications. Its bright f/2.8 constant maximum aperture affords consistent brightness throughout the zoom range and benefits working in available lighting conditions. The optical design incorporates a series of aspherical and low-dispersion elements, which suppress a variety of aberrations for improved sharpness and clarity. Individual elements are also multi-coated to resist flare and ghosting for greater contrast and color accuracy when working in bright or backlit conditions. Ultra-wide zoom is designed for DX-format Nikon F-mount cameras and provides a 16.6-30mm equivalent focal length range. Bright constant f/2.8 maximum aperture affords consistent brightness throughout the zoom range and offers improved control over the depth of field. Three aspherical elements, including two glass-molded elements and one P-MO hybrid element, help control spherical aberrations and distortions for sharper, more accurate rendering. Three SD (super-low dispersion) elements control color fringing and chromatic aberrations throughout the zoom range for greater clarity and color accuracy. Silent-Drive focusing Motor (SD-M) pairs with a GMR sensor and an internal focusing design to achieve fast, responsive, and precise performance. One-Touch Focus Clutch Mechanism avails quick switching between autofocus and manual focus settings by either pushing or pulling the focus ring. The water-repellent top coating makes wiping and cleaning the surface of the front glass element easier.