some detail ..
PMA 2007: Sigma has today announced one massive beast of a lens; the APO 200 - 500 mm F2.8 EX DG. This lens is stated by Sigma as being the worlds first Ultra-Telephoto Zoom Lens that offers an impressively fast F2.8 maximum aperture through its range. The lens also features and LCD panel with a readout of focal length and subject distance. If 500 mm isn't enough reach a dedicated 2x Tele Converter is supplied with the lens as standard and changes it into a 400 - 1000 mm F5.6. Combine that with a typical APS-size 1.5x FOV crop on a digital SLR and you've got either 300 - 750 mm F2.8 or a 600 - 1500 mm F5.6 (better have a good tripod). No news on price, availability or weight yet.
The world's first Ultra-Telephoto Zoom Lens that offers a fast aperture of F2.8 at 500mm focal length
The APO 200-500mm F2.8 EX DG is the world's first Ultra-Telephoto Zoom Lens that offers a fast aperture of F2.8 at 500mm focal length. It covers the widely used 200 to 500mm focal length range, and maintains its fast F2.8 aperture over the entire zoom range. Four SLD (Special Low Dispersion) glass elements provide excellent correction for all types of aberrations and produce a high level of optical performance throughout the entire zoom range.
Shooting distance and focal length can be viewed on the lens' LCD panel, which is an additional convenience for the photographer.
A filter can be inserted towards the rear of the lens, and a circular polarizing filter can be used with its ingenious rotation mechanism.
A dedicated APO TELE CONVERTER 2x EX DG II is supplied as a standard accessory with the APO 200-500mm F2.8 EX DG.
Its exclusive design minimises image degradation usually associated with teleconverters. When this dedicated teleconverter is used with the APO 200-500mm F2.8 EX DG lens, it becomes a large aperture 400-1000mm F5.6 AF Ultra-Telephoto Zoom lens.