Versatile telephoto zoom is designed for full-frame Canon EF-mount DSLRs, however can also be used with APS-C models where it provides a 112-320mm equivalent focal length range. Bright constant f/2.8 maximum aperture affords consistent performance throughout the zoom range and offers notable control over depth of field for working with selective focus techniques. One fluorite element and five ultra-low dispersion glass elements noticeably reduce color fringing and chromatic aberrations for high clarity and color fidelity. An Air Sphere Coating (ASC) has been applied to lens elements to reduce backlit flaring and ghosting for maintained light transmission and high contrast in strong lighting conditions. An Optical Image Stabilizer helps to minimize the appearance of camera shake by up to 3.5 shutter speed stops to better enable working in low-light conditions and with slower shutter speeds. In addition to the single-shot standard IS mode, a second mode is also available that it optimized for panning. A ring-type Ultrasonic Motor (USM), along with an internal focusing system, is employed to deliver fast, precise, and quiet autofocus performance as well as full-time manual focus override. Focus Limiter switch lets you constrain the focusing to two different ranges to suit different applications: 3.9′-infinity or 8.2′-infinity. Rounded eight-blade diaphragm contributes to a pleasing out of focus quality that benefits the use of shallow depth of field and selective focus techniques. A weather-resistant design protects the lens from dust and moisture to enable its use in inclement conditions. Additionally, fluorine coatings have also been applied to the front and rear lens elements for further protection against fingerprints and smudging. Removable rotating tripod collar is included and benefits working with the lens atop a tripod or monopod. Compatible with optional EF 1.4X and EF 2X teleconverters.