This Sigma 500mm f/4.5 EX DG APO HSM lens is an Apochromatic ultra-telephoto lens with a fast f/4.5 maximum aperture, and it incorporates two ELD (Extraordinary Low Dispersion) glass elements to reduce chromatic aberration to a minimum. Internal focus enables responsive and fast autofocus speed.
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.
By adding the optional Sigma APO teleconverter, you can use this lens as a 700mm f/6.3 MF ultra-telephoto lens with a 1.4x EX teleconverter, or as a 1000mm f/9 MF ultra-telephoto lens with a 2x teleconverter.