Canon 17-40mm F/4.0 Overview
- 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.