The Sigma APO 300mm f/2.8 EX DG HSM lens is an ultra compact Apochromatic telephoto lens with a fast f/2.8 maximum aperture, and incorporates two Extraordinary Low Dispersion glass elements to reduce chromatic aberration to a minimum. It incorporates internal focusing which enables responsive and fast autofocus speed. A detachable tripod socket and rotatable drop in filter holder are also included.The improved DG lens design corrects for various aberrations. This lens is specially coated to get the best color balance whilst cutting down on ghosting caused by reflections from the digital image sensor. The lens provides the utmost correction against lateral chromatic aberration, which is a serious problem for digital SLR cameras.With the use of the optional Sigma APO teleconverters, this lens can be used as a 420mm f/4 AF ultra-telephoto lens with a 1.4X EX teleconverter, or a 600mm f/5.6 AF ultra-telephoto lens with a 2X teleconverter. Hyper Sonic Motor for quiet & smooth AF with fulltime manual focus override,Two ELD glass elements reduce chromatic aberration to a minimum and also ensure sharp, quality images of high contrast,Internal focusing with a non-rotating front,A drop-in 46mm filter holder in the rear part of the lens barrel can be rotated to facilitate the use of filters, including a polarizing filter,Removable tripod collar,Built in front protective filter,The rounded 9-blade diaphragm opening makes out-of-focus elements appear more natural