The Sigma 500mm F4.5 DG APO HSM is a ultra telephoto prime lens designed for Full Frame sensors but may also be used with smaller APS-C size sensors with a corresponding effective increase in focal length to about 750 with most cameras. The 500mm is a unique focal length and its large fixed aperture of 4.5 makes it great for photographing wildlife. A Hyper Sonic Motor (HSM) ensure quiet, accurate and high speed autofocusing working together with an Inner Focusing system which enables additional speed and responsiveness while, the overall length does not change during focusing. Surprisingly compact for its focal length, the 500mm is approximately 14 inches long and weighs slightly less than 7 pounds. Two ELD (Extraordinary Low Dispersion) glass elements provide optimum color correction and sharpness throughout the entire zoom range and a new multi-layer lens coating technology and lens design formula reduce flare and ghosting. Rear insertion 46mm filters with provision for easy rotation of polarizing filters. Also, compatible with the Sigma APO Tele Converters to provide additional focal length as a 700mm F8 or 1000mm F11 lens.