Sigma 70 200mm f28 ex dg os hsm large aperture telephoto zoom lens incorporating sigmas original optical stabiliser function this large aperture telephoto zoom lens incorporating sigmas original optical stabiliser function covers focal lengths from 70mm to 200mm and offers a constant aperture of f28 over the entire zoom range the os function offers the use of shutter speeds approximately 4 stops slower than would otherwise be possible it makes shooting easy for many types of photography such as