This is an in-depth review of the Canon EF 200-400mm f/4L IS USM with a built-in 1.4x extender, a telephoto zoom lens targeted at enthusiast and professional action photographers. For many years, Canon users shooting serious wildlife and sports photography had come to accept that the only telephoto lenses on offer by Canon that achieved top of the line performance were their prime lenses. At the time, the only Canon zoom lens in the telephoto range was the Canon EF 100-400 f/4.5-5.6L IS, a solid, if unspectacular lens with an outdated design. On the other hand, and much to Canon users’ envy, Nikon had given its customers something wholly different in 2003 when they released the Nikon 200-400mm f/4G VR, a professional-quality constant aperture super telephoto zoom lens. While Nikon’s 200-400mm had its faults (namely lack of sharpness when photographing distant subjects), it was the perfect lens to take on an African Safari or to a sports game. With fast autofocus, a constant aperture and good sharpness all packaged into a zoom lens, the Nikon lens was perfect for situations which required versatility and the ability to change focal lengths, while still maintaining high image quality. Nikon’s monopoly on professional grade super telephoto zooms would thankfully change in 2011 when Canon announced the development of its own 200-400mm f/4 lens which was also going to be the first telephoto lens of its kind to utilize a built-in teleconverter.