EF 17-40mm f/4L USM

• Powerful ring-type ultrasonic monitor (USM) produces fast and silent autofocusing, Focuses as close as 11 inches, supports screw-in 77-millimeter filters or up to 3 gel filters. 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
• EF 17-40mm f/4L USM is suitable for Wedding/Nature Photography, Weather-resistant construction, Water and Dust Resistant measures 3.3 inches in diameter, 1-year warranty
• Purchase this product between May 1, 2016, and July 30, 2016, and get 13 months of free damage protection from Canon. The product must be registered within 30 days of the purchase date to be eligible
• 17 40 millimeters ultra-wide-angle zoom lens with f/4 maximum aperture for Canon SLR Cameras. Diagonal angle of view 104° 57° 30′
• 3 aspherical lens elements and super UD glass element create superior optics in all conditions, Closest focusing distance: 0.9 feet

From the manufacturer

L-series ultra-wide-angle zoom lens that’s ideal for both film and digital SLRs. Superior optics by the use of three Aspherical lens elements, in addition to a Super UD (Ultra-low Dispersion) glass element. Optical coatings are optimized for use with digital cameras. This lens focuses as close as 11 inches (0.28m), and offers both Canon’s full-time manual focus and a powerful ring-type USM for fast and silent AF. It has a constant f/4 maximum aperture and offers the choice of screw-in 77mm filters or a holder in the rear of the lens for up to three gel filters. Finally, it offers a weather-resistant construction.