Sigma's 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 Sigma SA, Canon and Nikon S.L.R. cameras features the ultra-quiet Hyper Sonic Motor (H.S.M.). This new 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 new lens are lead and arsenic free ecological glass.
The Sigma 800mm f5.6 EX HSM APO ultratelephoto lens incorporates two extraordinary low dispersion (ELD) glass elements, which help reduce chromatic aberration to the minimum limit. With a fast f5.6 aperture, this apochromatic lens also incorporates an internal focusing system to give you fast, responsive autofocus speed. The ultraquiet hypersonic motor (HSM) lets you shoot pictures without disturbing your subjects. Polarizing filters are extremely easy to use with this lens because of its rotary filter holder, located in the rear part of the lens barrel. The optic materials are lead-free and arsenic-free ecological glass. This model is dedicated to Nikon AF SLR cameras.