Canon EF 17-40mm f/4L USM Overview

Spanning a versatile wide-angle range, the EF 17-40mm f/4L USM Lens is a Canon L-series zoom featuring a constant f/4 maximum aperture along with a sophisticated optical design and durable construction. One Super UD element is featured, along with three aspherical elements, which help to reduce both chromatic and spherical aberrations in order to realize high sharpness, clarity, and color accuracy. A Super Spectra coating has also been applied to suppress flare and ghosting for improved contrast in difficult lighting conditions. Complementing the imaging capabilities, this wide-angle zoom also features a ring-type USM and internal focusing mechanism to afford quick, quiet, and accurate autofocus performance, as well as full-time manual focus override. Additionally, this lens is weather-sealed for use in trying environmental conditions.

• Wide-angle zoom is designed for full-frame Canon EF-mount DSLRs, however can also be used with APS-C models where it provides a 27.2-64mm equivalent focal length range.
• Constant f/4 maximum aperture maintains consistent illumination throughout the zoom range.
• One Super Ultra-Low Dispersion glass element noticeably reduces color fringing and chromatic aberrations for high clarity and color fidelity.
• Three aspherical elements minimize spherical aberrations and distortions for improved sharpness and accurate rendering.
• Super Spectra coating has been applied to individual elements to minimize ghosting and flare for greater contrast and color neutrality when working in strong lighting conditions.
• A ring-type Ultrasonic Motor (USM), along with an internal focusing system, is employed to deliver fast, precise, and quiet autofocus performance as well as full-time manual focus override.
• Rounded seven-blade diaphragm contributes to a pleasing out of focus quality that benefits the use of shallow depth of field and selective focus techniques.
• As a member of the esteemed L-series, this lens is sealed against dust and moisture for working in inclement environmental conditions.
• In addition to the front 77mm filter ring, this lens also has a rear filter holder for up to three cut gel filters.