The Sigma 500mm f/4.5 Ex DG APO HSM Auto Focus Telephoto Lens is a ultra-telephoto lens that has a fast maximum aperture and also features a super multi-layer coating, which optimizes the characteristics of digital SLR cameras. Two ELD glass elements in the front lens elements reduce chromatic aberration to a minimum and also ensure sharp, quality images of high contrast. The overall length of the lens does not change during focusing, ensuring convenient handling and ease of use. The AF drive for Canon SLR cameras features Sigma’s ultra-quiet and high-speed Hyper Sonic Motor (HSM). It also features a drop-in 46mm filter holder in the rear part of the lens barrel, which can be rotated to facilitate the use of filters, including a polarizing filter. By adding an APO teleconverter (optional extra), you can use this lens as a 700mm F6.3 MF ultra-telephoto lens with a 1.4x Ex teleconverter, or as a 1000mm F9 MF ultra-telephoto lens with a 2x teleconverter.