HSM stands for Hyper Sonic Motor. It is a new type of motor used in some of Sigma’s newer lenses. The technology employed is similar to that used in certain lenses made by other camera manufacturers. The benefits of HSM system are: virtually silent autofocus function, very quick responsive autofocus function. Sigma is the only independent lens maker offering lenses with this technology. We have a number of HSM type lenses for Canon and Sigma AF cameras, and we also have several HSM lenses for Nikon AF cameras (N55, N65, N70, N75, N80, N90, N90S, F100, F4s, F5, D1, D1X, D1H, D100 and D70, as well).