The Sigma 105mm f2.8 EX DG OS HSM Macro Lens for Canon EF is a large aperture medium telephoto macro lens offering advanced performance for close-up photography. Sigma’s own proprietary OS (Optical Stabilizer) system enables handheld close-up photography. A Special Low Dispersion (SLD) lens and one high refractive index SLD lens provide excellent correction for all types of aberration and distortion. A floating focusing system moves two different lens groups in the optical path to different positions. This system compensates for astigmatic aberration and spherical aberration and provides extremely high optical performance from infinity to 1:1 Macro.