The Sigma 17-50mm f/2.8 EX DC OS HSM Zoom Lens is an incredibly versatile, lightweight, and compact lens designed specifically for digital SLR cameras with APS-C size sensors. The lens has a fast f/2.8 maximum aperture throughout the entire zoom range. It features a construction of 17 elements in 13 groups with glass that corrects for flare, ghosting and all types of aberrations. It produces high contrast and sharp images throughout the zoom range even at its maximum aperture.
Sigma's OS (Optical Stabilization) feature allows you to shoot at shutter speeds approximately 4 stops slower than would otherwise be possible. This means your images will look sharper, even when shooting without a tripod in low existing light or at maximum range with a flash. This lens is also equipped with Sigma's Hyper-Sonic Motor (HSM) which provides for fast and quiet autofocusing.
The Sigma 17-50mm f/2.8 is ideal for many photo opportunities particularly landscapes and portraits, but with its wide focal range and a close focusing distance down to 11" (28cm) you can capture images with unique perspectives. It will quickly become one of the most important lenses in your gear bag.