This lens from Canon is a high performance, water-resistant, ultra wide-angle L-series zoom lens. An f/2.8 maximum aperture is effective in low light situations and offers shallow depth of field focus control. 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. Its ultrasonic motor (USM) and improved AF algorithms will help the lens to focus faster and quieter. Precise manual focus is supported even in One Shot AF mode and a truly round aperture results in pleasing background blur.
All of the “L” lenses deliver optical performance equal to similar fixed focal lengths lenses and provide tight seal structures for dust and water resistance. Distortions and aberrations are remarkably small for a lens of such amazing capabilities. An included petal-style lens hood keeps unwanted light from entering the lens and causing flare and it offers a degree of protection against impact and the elements.