The Sigma 17-50mm f/2.8 EX DC HSM Zoom Lens for Sony DSLRs with APS-C Sensors is a versatile, lightweight, and compact lens designed specifically for Sony A-mount and Minolta digital SLR cameras with APS-C size sensors. The lens has a fast f/2.8 maximum aperture throughout the entire zoom range and its 35mm focal length equivalency is 25.5 - 75mm. It features a construction of 17 elements in 13 groups with glass that corrects for aberrations and multi-layered lens coating to minimize flare and ghosting. It produces high contrast, sharp images throughout the zoom range even at its maximum aperture.
This lens is equipped with Sigma's Hyper-Sonic Motor (HSM) which provides fast and quiet auto focusing, which is ideal when shooting video.
This Sigma 17-50mm f/2.8 lens does not contain the OS (Optical Stabilization) designation because Sony Alpha DSLR's equip their camera bodies with image stabilization technology.
Note: Autofocus does not work properly with the Sony Alpha SLT-A65 and SLT-A77 DSLR digital cameras. A free update is available from Sigma to correct this phenomenon and future production of this lens will be fully compatible with these cameras.