The newest 120-300mm F2.8 DG APO OS EX HSM lens by Sigma includes Optical
Stabilization (Sigma calls it OS) which becomes essential for lenses included in this focal range if you want hand-hold telephoto photography and to select shutter speeds up to 4 stops less than could otherwise be feasible. This Sigma also includes a new splash-proof facet that prevents dust and moisture from collecting inside the lens. There is a single SLD and a pair of FLD glass elements to provide maximum rectification of chromatic aberration.
A super multi-layer lens coat cuts down on flare and ghosting, while the lens design encompasses inner focusing plus inner zooming to ensure sharp photos throughout the whole zoom range. The optical performance has been improved to provide excellent tweaking of any sagittal coma flare while making certain of ultra-high resolution that is comparable to a lens with a focal length that is fixed. The Hyper Sonic Motor (Sigma calls it HSM) provides quiet high speed
auto focusing , while providing all-the-time over ride for manual focus. A truly unique lens which is rare in the photo manufacturing industry, as it's a one of a kind professional zoom lens which also sports a fast aperture.
Just about all professionals have a traditional 300mm 2.8, although they must carry around a shorter zoom for those instances when subjects move in closer resulting in futzing around changing lenses or packing a second camera. The remarkable Sigma zoom lens allows you to instantly ascertain the composition you desire without having to switch your vantage position. Imagine shooting courtside at a basketball game with the
flexibility to zoom in the face or hand of a player and then quickly zoom back to your previous position capture all of the player getting his shot. With the Sigma 120-300mm you can do just that. The lens aperture stays at a constant F2.8 during the total zoom range. By adding an APO tele converter (which is optional) you can end up with an autofocus ultra telephoto zoom lens. 
Apr 18, 2011
HSM allows the lens will autofocus on Nikon D40/D40x,
Nikon D60, Nikon D3000,
Nikon D3100,
Nikon D5000 and Nikon D5100
