The Sigma APO 800mm f5.6 EX is one of the EX Series lenses. It is an Apochromatic ultra-telephoto lens with a fast F5.6 maximum aperture, and incorporates two Extraordinary Low Dispersion glass elements (Abbe number 90.3), to reduce chromatic aberration to minimum limit. It also incorporates internal focusing which enables responsive and fast auto focus speed. The AF drive for Canon SLR cameras features the ultra-quiet Hyper Sonic Motor (HSM). This lens also incorporates a rotary filter holder in the rear part of the lens barrel, which enables the use of a polarizing filter. Sigma's dedicated APO EX Tele Converter 1.4x MF and 2x MF can be used with this lens. The lens materials used in this lens are lead and arsenic free ecological glass.