This 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 & one high refractive index SLD lens provide excellent correction for all types of aberration & distortion. A floating focusing system moves two different lens groups in the optical path to different positions. This system compensates for astigmatic aberration & spherical aberration & provides extremely high optical performance from infinity to 1:1 macro. The super multi-layer coating reduces flare & ghosting, providing high contrast images. It is also possible to use this lens with Sigma's APO teleconverters. The HSM (Hyper Sonic Motor) ensures quiet & 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.