The sigma apo macro 180mm f28 ex apo dg os hsm is a fast telephoto macro lens with a magnification ratio of 11 and a large maximum aperture of f28 sigmas optical stabiliser os function and the wide f28 aperture allows for faster shutter speeds and a narrow depth of field enabling photographers to emphasize the subject three fld f low dispersion glass elements provide excellent colour correction for colour aberrations and super multi layer coating reduces flare and provides sharp imag