Supersonic means just above the human hearing range, ultrasonic means far above it but below the range of radio waves. Usually that is something like 15kc to 30kc for supersonic, and 30kc to 100kc for ultrasonic waves. It is the frequency that is important to the label, not the media. Note that the terms are used differently when used for aircraft rather than electronics.
-- graywolf http://www.graywolfphoto.com http://webpages.charter.net/graywolf "Idiot Proof" <==> "Expert Proof" ----------------------------------- Toralf Lund wrote: >> On the low-end, AFD was replaceed by the micro-motor drive, which is >> faster with small, light lenses but not powerful enough for anything >> heavy. It's essentially a small high-speed motor. >> > It's essentially a normal DC motor with an ironless core, isn't it? (Or > am I referring to something else?) > > This is surely technology one might equally well use in an in-body motor. >> Then Canon introduced the USM Ken describes, with the focus ring being >> an electronic control (which was also the case in certain early AFD >> lenses, a couple even lacked MF capability entirely)meaning no focusing >> without power. These are the lenses that made Canon's reputation for >> fast AF. They would later be replaced by 2 different types of USM. The >> first is Ring-Type USM, which adds a clutch mechanism for mechanical >> full-time manual focus and works faster, it's essentially an improved >> version of the original USM, these lneses also provide distance info for >> flash exposure. The second is called micro-motor USM, and is merely a >> conventional micro-motor driven by ultrasonic AC. > Surely that does not make it an "ultrasonic motor"? I mean, doesn't the > term "ultrasonic" usually refer to (acoustic) vibrations that are > actually driving the motor? Applied to an AC voltage it seems rather > meaningless... > > Apart from that, thanks for an interesting overview. > > - Toralf > -- PDML Pentax-Discuss Mail List [email protected] http://pdml.net/mailman/listinfo/pdml_pdml.net
