The Canon EF 16-35mm f/2.8L II USM Autofocus Lens is a high performance, water-resistant, and ultra wide-angle L-series lens. The optical design has been improved to offer better edge-to-edge image quality. In addition, it features 3 high-precision aspherical lens elements, each of a different type: ground, replica and GMo. Improved AF algorithms will help the lens to focus faster and quieter. All of the "L " lenses deliver optical performance equal to similar fixed focal lengths lenses, and the USM lenses do this with silent, high-speed focusing. Distortions and aberrations are remarkably small for a lens of such amazing capabilities. Entirely internal focusing and zooming movement Ring-type USM provides ultra-quite, super-fast, precision auto focusing and predictive tracking Fulltime manual focus override (even in AF mode) Circular aperture diaphragm produces brilliant out-of-focus characteristics