USM = Ultra-Sonic Motor. What that means is instead of using a DC motor they use an AC motor that works at ultrasonic frequencies (100khz and above). The extremely high frequency of the power source (generated electronically) allows the motor to be very small and light. That means the motor can accelerate much faster than a low frequency or DC motor. Used in a lens that translates into a lighter, and faster focusing, lens . However since the motor has to move a mass of glass the overall improvement is only incremental in the real world. HSM (Hyper-Sonic Motor) means the same thing. 10% real improvement, 90% hype <g>
Ciao, Graywolf http://pages.prodigy.net/graywolfphoto ----- Original Message ----- From: "Gregory L. Hansen" <[EMAIL PROTECTED]> To: <[EMAIL PROTECTED]> Sent: Monday, March 17, 2003 12:37 PM > I don't care about USM, but other people seem to, so > maybe that's just because I don't understand it well enough to want it. >
