Doug Franklin wrote: > Adam Maas wrote: > > >> Not always. SDM lenses hunt a lot less because they won't overshoot >> the mark, they are in effect stepper motors, and are told how far to >> turn the lens, screwdriver AF tends to overshoot more. >> > > Are the in-body motors on the screw-drive cameras not stepper motors? > I've never checked the actual motors, but I'm fairly sure there are "shaft encoder" components within the lens, which tells me that the setup is designed for a simple DC motor. They might still have swapped that for a stepper in later models, but somehow I don't think they have. > If not, is it because steppers would be significantly more expensive? > I would assume that they were in the days when AF was introduced. Or perhaps it was hard to put the circuitry required to drive them (or the motors available) inside the camera, or difficult to implement the software on the processors of that era...
Today I can't imagine there would be any problems, or that much of an added cost, but now that everything needed to control a simple motor is there anyway, maybe even a minor price increase isn't thought to be justified... I'm only speculating, of course ;-) - T -- PDML Pentax-Discuss Mail List [email protected] http://pdml.net/mailman/listinfo/pdml_pdml.net to UNSUBSCRIBE from the PDML, please visit the link directly above and follow the directions.
