Constant f/4 aperture Image stabiliser Ultrasonic motor Having a constant aperture alongside the L series construction makes the Canon EF 70-200mm f/4L IS USM a highly impressive lens for distance work as well as robust enough for the most demanding of photographers. Having a constant aperture means regardless of the focal length a bright, fast aperture is possible which makes it possible to shoot in limited light without affecting image quality. The image stabiliser can detect the direction of movement so the unused axis can be disabled, and when the lens is on a tripod the feature can be disabled altogether. The Ultrasonic motor is both quiet and rapid, which is useful for sports and wildlife photography, giving yet another reason to purchase this excellent lens. A fast, and sharp telephoto zoom lens, a perfect affordable alternative to the f/2.8 version.