The Sigma 17-50mm F2.8 EX DC OS HSM is a wide to standard zoom lens designed for APS-C DSLRs. Equipped with a Hyper Sonic Motor (HSM) and an Optical Stabilizer (OS), the 17-50mm boasts a large fixed 2.8 aperture throughout the entire zoom range. An OS allows for easier handheld shooting while the HSM ensures quick, accurate and consistent autofocusing. FLD glass elements (with performance equal to fluorite) along with two glass mold elements and one hybrid aspherical lens provide excellent correction of aberrations and allow for incredibly sharp images with great contrast. Super Multi-Layer coating reduces flare and ghosting while the lightweight and compact construction make it a necessary addition to any camera bag.