Wide-angle zoom 16-35mm lens is compatible with full-frame Canon EF-mount DSLRs, as well as APS-C-sized models where it will provide a 25.6-56mm equivalent focal length range. Constant f/2.8 maximum aperture offers consistent performance and excellent light transmission throughout the zoom range. Two large-diameter glass-molded dual-surface aspherical elements and one ground aspherical element help to minimize distortions and spherical aberrations throughout the zoom range in order to maintain edge-to-edge sharpness and illumination. Two ultra-low dispersion elements are used to minimize chromatic aberrations as well as eliminate color blurring around the edges of subjects. Both a Subwavelength Coating (SWC) and an Air Sphere Coating (ASC) have been applied to lens elements to reduce backlit flaring and ghosting for maintained light transmission and high contrast in strong lighting conditions. A ring-type Ultrasonic Motor (USM), along with an internal focusing system, high-speed CPU, and optimized AF algorithms, are employed to deliver fast, precise, and near-silent autofocus performance as well as full-time manual focus override. As a member of the esteemed L-series, this lens is sealed against dust and moisture for working in inclement environmental conditions. Protective fluorine coating has been applied to the front bulbous element to resist fingerprints and smudges and to make cleaning significantly easier. Rounded nine-blade diaphragm contributes to a pleasing out of focus quality that benefits the use of shallow depth of field and selective focus techniques.