Characterized by its versatile zoom range and bright design, the Sigma SA-mount 17-50mm f/2.8 EX DC OS HSM from Sigma 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. Additionally, the lens is distinguished by its sleek profile, making it an ideal lens for walkaround and travel shooting.Standard zoom lens is designed for APS-C-format Sigma SA-mount cameras and provides a 25.5-75mm equivalent focal length range.Constant f/2.8 maximum aperture is well-suited for working in low-light conditions and also provides greater control over the focus position when using shallow depth of field techniques.Two F Low Dispersion (FLD) elements are featured in the optical design, and help to reduce color fringing and chromatic aberrations for improved clarity and color accuracy.Three aspherical elements are used to help limit distortion and spherical aberrations and also contribute to greater overall sharpness and accurate rendering.Super Multi-Layer Coating has been applied to individual elements to minimize flare and ghosting for improved contrast and color accuracy when working in strong lighting conditions.Hyper Sonic Motor (HSM), along with an internal focusing design, realizes quick and quiet autofocus performance as well as full-time manual focus override.Minimum focusing distance of 11" and a 1:5 maximum magnification ratio benefits working with close-up subjects.Optical Stabilizer system minimizes the appearance of camera shake to benefit making sharper imagery when shooting handheld.Rounded seven-blade diaphragm contributes to a pleasing bokeh quality.