Sigma 50-200mm f/4.0-5.6 DC IF SLD Optical Stabilized (OS) Lens with Hyper Sonic Motor (HSM) for Canon Digital SLR Cameras Optical Stabilization - Sigma's own OS System Inner Focusing System - Eliminates front lens rotation; suitable for use w/circular polarizing filters Compact, Telephoto Zoom Lens High Image Quality - SLD glass elements with inner focusing High Magnification - 1 - 4.5 magnification, exclusively designed for digital SLRs