The Canon EF 100-400mm f/4.5-5.6 L IS USM Lens has an excellent focal length range that includes the longest focal length found in a Canon zoom lens - 400mm. This long focal length and focal length range combine with very good image and build quality to make the 100-400 one of the most popular serious wildlife and sports lenses Canon sells.  To say that the Canon EF 100-400mm f/4.5-5.6 L IS USM Lens is a member of the Canon L Series quickly says a lot about this lens. Weighing 3 lb (1,380g) and measuring 3.6" x 7.4" (92.0 x 189.0) (DxL retracted), the 100-400 is solidly built and feels like it.