No, I didn't want to use Arduino for processing the autofocus, but use the motor of a lens manually, that has autofocus.
As I tried to mention in the end of my question, I get a signal on a photomultiplier, at which I look. So the processing is actually done by human 
So I need the message protocol for the lens (or the mount?).
I guess, that is mostly a secret from the producer of the lenses? 