The Sigma 105mm f/2.8 is a large aperture medium telephoto macro lens offers advanced performance of 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.The Super Multi-Layer Coating reduces flare and ghosting, providing high contrast images. It is also possible to use this lens with Sigma’s APO TELE CONVERTERS. The HSM (Hyper Sonic Motor) ensures quiet and high speed autofocus as well as full-time manual focus capability. This lens features a rounded 9 blade diaphragm creating an attractive blur to the out of focus areas of the image.