Sigma 50-500mm f/4-6.3 EX DG HSM APO
(From Sigma lens literature) This high zoom ratio lens is optimized for digital SLR cameras and capable of covering a wide range of focal lengths from 50mm standard to 500mm ultra telephoto.
The advanced optical design is optimized for digital SLR cameras. In addition, the new super coating on each glass surface produces superb color rendition, while reducing flare and ghosting.
This lens uses four pieces of SLD (the special low dispersion) glass for excellent correction of color aberration throughout the entire zoom range.
The HSM models (the HSM is only available for AF Canon, Nikon and Sigma Mounts) provide quiet high-speed AF function, as well as full time manual focus capability.
This lens also features a Zoom Lock device to eliminate "Zoom Creep" when the lens is tilted down. When the lens is set to the 50mm focal length, it is remarkably compact and provides easy handling. The tripod mount is composed of magnesium, to minimize total weight and also it is easy to grip and carry the lens due to ergonomic design of the tripod mount.
Non-rotating front lens elements, due to rear focus mechanism make possible the use of a custom bayonet petal-type hood, which prevents extraneous light from degrading the image quality. This mechanism also allows the use of circular polarizing filters, since the front barrel does not rotate during focusing or zooming.
By adding an APO teleconverter (sold separately), you can use this lens as a 140-700mm ƒ/7.3-8.8 MF ultra-telephoto zoom lens with a 1.4X EX teleconverter, or as a 200-1000mm ƒ/10.4-12.6 MF ultra-telephoto zoom lens with a 2X teleconverter. (Teleconverters can be used in 100mm-500mm focal length range).