The Sigma 17-50mm f/2.8 EX DC OS HSM covers a wide-angle to portrait-length range and features a constant f/2.8 maximum aperture to excel in available light conditions. The optical design incorporates a pair of low dispersion elements along with a trio of aspherical elements to reduce a variety of aberrations and promote greater sharpness and clarity. A Super Multi-Layer Coating is also used to suppress flare and ghosting for improved contrast and color accuracy. Benefitting the optics, a Hyper Sonic Motor affords quick and quiet autofocus performance while an Optical Stabilizer minimizes the appearance of camera shake for sharper handheld shooting.