The 16-35mm f/4 L IS USM is a high-performance, wide-angle zoom lens with wide-ranging flexibility, and a fixed f/4 aperture providing clear, sharp results. Whether you are shooting in wide open places or confined spaces, this is a must-have all-purpose lens. Quickly focus using the powerful, fast and silent autofocusing (AF) performance of ring-type Ultrasonic Motor (USM.) Two Ultra-low Dispersion (UD) elements minimise chromatic aberration and eliminate colour blurring, for the highest image quality possible. Both ghosting and flare have been minimised by the lens' Super Spectra Coating and it has been weather-sealed.