The Sigma 17-50mm f2.8 EX DC OS HSM lens is an image-stabilised, fast standard zoom for digital SLR cameras with an APS-C sized sensor. The lens covers a focal length from 17mm wide angle and offers a large aperture of f/2.8 throughout the entire zoom range, making it ideal for many types of photography such as portraiture and landscapes. Alongside Sigma's Optical Stabilizer (offers the use of shutter speeds approximately 4 stops slower than would otherwise be possible), the 17-50mm OS lens also includes a hypersonic autofocus motor, for quicker, quieter focusing.