Sigma has today announced that it is to release updated HSM motor driven versions of the DC 17-70 mm and DC 18-50 mm lenses on the Nikon lens mount. For those unfamiliar with the numerous lens acronyms, HSM stands for Hyper Sonic Motor, (also known as Ultrasonic motor, Silent Wave Motor or even Sonic Direct-drive Motor) and is a faster, quieter and often more compact motor system for lenses. Essentially this should mean quieter and faster focusing.

Source: Debbie