This large-aperture EF-S Series standard zoom lens features an optical system consisting of 19 lens elements in 12 groups. Three aspherical lens elements (one glass-molded and two replica surfaces) efficiently compensate for aberration fluctuations over the entire zoom range while enabling a large f/2.8 aperture and high image quality. Two UD lenses also reduce secondary chromatic aberrations to produce high-resolution, high-contrast images without colour aberration bleeding around subject edges. The inner focus and a ring-type USM achieve silent, high-speed autofocusing, while full-time manual focus override offers excellent operability by enabling users to tweak focusing without exiting the autofocusing mode. Now it’s easier to determine the ideal focus when shooting portrait and close-up photos with a large aperture setting. A circular aperture diaphragm contributes to beautiful background blur, and the optimized lens configuration and coating reduce the flare and ghost so common with digital cameras. This outstanding optical performance and operability is further enhanced by an Image Stabilizer that reduces the amount of camera-shake blur to roughly that of a 3 f-stop faster shutter speed*¹. Clearly, this standard zoom lens meets the stringent requirements of professionals. The lens mechanism is designed to ensure that it fits only EOS DIGITAL SLR cameras designed to take EF-S lenses, and it is equipped with a special attachment indicator and protective rubber mount ring to prevent mistaken attempts to attach it to other EOS SLR cameras, and to prevent damage to the camera body.