Let's say that KAF3 is coming and does support USM. USM lenses are made and sold.
OK... so, again, my limited knowledge says that USM puts the AF motor in the lens, and not the body. This means that the screw-drive method for the camera communicating to the lens the focus is useless. Is it then possible that USM lenses will be AF backwards compatable with any body that doesn't not support KAF3? I suppose there'd be a way for the body to tell the lens via the little screw how to focus the lens, but I can't imagine it would be fault proof and cheap, and thus probably not the most ideal answer, especially for EVERY lens to be backwards comptable with anything not KAF3? Obviously, this is only a hindrance to AF use of the lens.. -- http://www.infotainment.org <-> more fun than a poke in your eye. http://www.eighteenpercent.com <-> photography and portfolio.
