Sigma 500mm f4.5 EX Apo is one of the EX Series lenses. It is an Apochromatic ultra-telephoto lens with a fast F4.5 maximum aperture, and it incorporates two Extraordinary Low Dispersion glass elements (Abbe number 90.3), to reduce chromatic aberration to a minimum. It incorporates internal focusing which enables responsive and fast auto focus speed. The AF drive for Sigma SA, Canon and Nikon S.L.R. cameras features Sigma's ultra-quiet Hyper Sonic Motor (H.S.M.). It also features a rotatable drop-in filter holder in the rear part of the lens barrel, which facilitates the use of filters, including a polarizing filter. Sigma's dedicated APO Tele Converter 1.4x MF and 2x MF can be used with this lens (in case of Canon EOS3 the 1.4x teleconverter can also provide the AF function). The lens materials used in this new lens are lead and arsenic free ecological glass.