I am not a mechanical engineer who could confirm your claims but what I meant was where does the "ultrasonic" or "hypersonic" came from were it not for the piezo-electric effect ? (You apply a certain electric potential to a crystal and that crystal vibrates. Conversely you apply pressure to that crystal and you get a electrical current back.)
In normal motors, we know it, the movement came from Faraday's discovery, a force results when an electric current flows through a wire in a magnetic field. Maybe there is a third technology in common use, cheap to manufacture, that I don't know of. But the two I cited above are ways you can convert electrical energy to mechanical movements. And piezo-electric motors came in a huge variety with different applications and different ways to drive them. Some would be linear actuators requiring a very high DC voltage like you said. In a typical Canon USM lens no huge movement is needed. The ring just vibrates at an ultrasonic frequency. Some other ring or whatever would convert the vibration to rotational movement. As for how exactly, I am no Canon engineer... I don't recall the URL but I read a site dismantling a Canon USM lens and the internal design of the USM motor looks very simple and very elegant. Hype or not, it is some cool stuff. But I wonder why a typical Pentax user would need that ? You wouldn't expect a Pentax to do everything a Canon does, exactly like I wouldn't expect a Canon to do everything a Pentax does. Let me phrase it in some other way. If Pentax has USM will they have an excuse 10 years from now to drop the in-body focusing motor altogether an leave all the current AF lenses obsolete... in much the same way they are now doing to the K mount of 1976 ? If USM really matters to you you would have switched to Canon more than 10 years ago. That said some Canon users really needs USM when he/she is covering some race event with a 500/4.5L lens... or when doing stealth photography requiring quietness. -- Bo-Ming Tong ----- Original Message ----- From: T Rittenhouse <[EMAIL PROTECTED]> Date: Tuesday, August 26, 2003 9:32 pm Subject: Re: My *ist film review > Ultrasonic motors are not neccessarily piezo-electric. In fact I > do not > think piezo-electric motors are ultasonic motors unless the term > is being > used for the crystal that converts DC into ultrasonic AC. What I > know as a > piezo-electric motor is something that has a very very limited > movement as > it is simply the deflection of a crystal element converted to > mechanicalmovement. In fact, I thought (never actually researched > it) that they were > simply using a linear ultra-sonic (100kc or so) motor to move a > few elements > in the lens for focusing. From what you are saying Ultra (or > Hyper) sonic is > just advertising hype like Turbo has become. > > Ciao, > Graywolf > http://pages.prodigy.net/graywolfphoto > > > ----- Original Message ----- > From: "Bo-Ming Tong" <[EMAIL PROTECTED]> > To: <[EMAIL PROTECTED]> > Sent: Tuesday, August 26, 2003 11:46 PM > Subject: Re: My *ist film review > > > > Most consumers don't know what is the piezo-electric effect, on > which> USM, HSM, silent motor or whatever other acronyms are based > anyway. But > > no I don't think it makes sense, at least hype-wise to put a > > piezo-electric motor in the body, instead of a normal one. The > advantage> of a piezo-electric motor are: 1, a lot of torque with > little movement, > > 2, save space in a lens because the motor can be a big ring, and > 3, no > > gears needed but direct transfer of motor movement to focusing > helicoil,> for silent operation. Since you need an AF shaft from > the body to drive > > the AF lens anyway, what you really need are 1, fast rotation > with less > > emphasis on torque, 2, save space in a camera body because the > camera> body is not cylindrical you would rather be using a small > normal motor > > instead of a big ring, and 3, the AF shaft transfer motor movement > > anyway so the quietness advantage is lost. > > > > But hey, who cares. I am happy with Pentax bodies with or without > > piezo-electric motors. > > > > T Rittenhouse wrote: > > > How do you know they haven't gone to a hyper (or ultra) sonic > motor. I > can > > > think of no reason why one could not be put in the body. It > would give > you > > > 90% of the performance for 10% of the cost. Pentax is just the > sort of > > > company that would do that without hyping (pun intended) it. > > > > > > Ciao, > > > Graywolf > > > http://pages.prodigy.net/graywolfphoto > > > > > --- > Outgoing mail is certified Virus Free. > Checked by AVG anti-virus system (http://www.grisoft.com). > Version: 6.0.512 / Virus Database: 309 - Release Date: 8/20/03 > > >
