Sigma 17-50mm f/2.8 EX DC OS HSM Zoom Lens for $429.99 shipped. Here is a screenshot for your reference. The 17-50mm f/2.8 offers Sigma’s OS System (Optical Stabilization) that allows shooting at shutter speeds approximately 4 stops slower than would be otherwise possible. It is constructed with 17 elements in 13 groups and features FLD (“F” Low Dispersion) glass. Most places have it for about $569.