17-40mm ultra-wide-angle zoom lens with f/4 maximum aperture for Canon SLR cameras. 3 aspherical lens elements and super UD glass element create superior optics in all conditions. Powerful ring-type ultra-sonic monitor (USM) produces fast and silent autofocusing. Focuses as close as 11 inches; supports screw-in 77mm filters or up to 3 gel filters. Suitable for Wedding/Nature Photography, Weather-resistant construction; measures 3.3 inches in diameter