The Sigma 200-500mm f/2.8 EX DG APO IF Lens is a massive ultra-telephoto zoom lens that offers an impressive fast f/2.8 aperture throughout its entire zoom range, all the way up to 500mm. Combined with the included dedicated high-quality 2x teleconverter, this lens can be converted for use as a 400-1000mm f/5.6 lens. Now combine this with an APS-C sized digital SLR camera, and you're looking at approximately a 300-750mm f/2.8, or a 600-1500mm f/5.6 (with 2x teleconverter) lens.