The Canon EF 100-400mm F4.5-5.6L IS Lens is a stabilized super-telephoto zoom lens for Canon’s full-frame and APS-C digital SLRs. One of the older L-series lenses in Canon’s current lineup, the 100-400mm has long been a favorite of enthusiast photographers working in the sports and wildlife fields, and it is compatible with Extenders 1.4x II and 2x II for even more reach (albeit with a penalty in maximum aperture and critical image quality). The lens is weather-sealed, and its push-pull zoom action has a friction control. The downside of the push-pull design is that it tends to suck in dust, over time. Optical construction includes fluorite and Super UD-glass elements.