The Sigma 120-400mm F4.5-5.6 DG APO OS HSM is a telephoto zoom 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 180 to 600mm with most cameras. It’s large telephoto zoom range plus its compact size of a mere 8 inches and weight of only 3.6 pounds, make it a great all purpose travel lens. A Hyper Sonic Motor (HSM) ensure quiet, high speed, and accurate autofocusing working with an Optical Stabilizer (OS) which compensates for camera shake when shooting hand-held. Three SLD (Special Low Dispersion) glass elements provide optimum color correction and sharpness throughout the entire zoom range. The 120-400 F4.5-5.6 is compatible with Sigma APO teleconverters.