Toralf Lund wrote: >>Yet another post that misses the most important point. >> >>Those two additional contacts are *power* contacts. That's all. >>There's no signalling going on over those contacts, so there's no >>need to play games with polarities, pulse modulation, or the like. >> >>They are there solely to provide power to electric motors; more >>power than is needed for the CPU and other circuitry in the lens. >> > > As I asked elsewhere, would there necessarily be any extra circuitry in > the lens? Or any need for additional signals? Or might there simply be a > plain, old motor control via the power alone. - And processing in the > camera, based on encoder feedback from the lens. I think that's there > already in the current AF interface, but I could be wrong. > > I'm not sure what you are referring to when you talk about pulse > modulation or polarities, but if you are thinking about step-motors, > note that the ones I've programmed are actually controlled via the power > input, too - but using 4 lines instead of just 2. And they are > current-controlled, not voltage-controlled. > > I guess what I'm saying is that even if they put the motor in the lens, > they might keep the motor's controller in the body - thus having no need > for extra "messages" to the lens. > > - Toralf >
USM, at least as implemented elsewhere, uses a stepper-type motor which is controlled by in-lens circuitry, not the camera body. The camera tells the lens how far to turn then the lens does so. This requires a level of in-lens circuitry beyond what is currently there (and is the reason for the problems with Sigma lenses and newer Canon and Nikon bodies). -Adam -- PDML Pentax-Discuss Mail List PDML@pdml.net http://pdml.net/mailman/listinfo/pdml_pdml.net
