The EF-S 17-55mm f/2.8 IS USM from Canon pairs the 27.2-88mm equivalent focal length range with a bright f/2.8 constant maximum aperture. Benefitting this design is a sophisticated optical layout, which includes both Ultra-Low Dispersion glass and aspherical elements to significantly reduce chromatic and spherical aberrations for improved clarity and sharpness throughout the zoom range. Also complementing handling is a sophisticated ring-type USM, which provides quick, quiet, and accurate autofocus performance along with a full-time manual focus override. Bright constant f/2.8 maximum aperture affords consistent illumination throughout the zoom range and also affords greater control over the depth of field for working with selective focus techniques. Super Spectra coating has been applied to individual elements to minimize ghosting and flare for greater contrast and color neutrality when working in strong lighting conditions. A ring-type Ultrasonic Motor (USM), along with an internal focusing design and optimized focusing algorithms, is employed to deliver fast, precise, and quiet autofocus performance as well as full-time manual focus override.