Many people have reported some Sigma lenses took longer to lock focus (tend
to hunt more). It seems that the distance and focal length data are required
for AF as well, and those data are held by a chip inside the AF lenses.
Alan Chan
http://www.pbase.com/wlachan
So the answer is that the camera possess the algorithms for AF but the
performance is based both on the algorithms and how responsive the lens
mechanism is? If that is correct then a lens that seems to "hunt" more than
another is not directly at fault? It is the camera algorithms not being
able to adequately handle the responsiveness of the lens? Interesting. Of
course you would still want to avoid such a lens because it is the system
as a whole that is important and therefore an unresponsive lens that causes
the camera to hunt is still a bad thing regardless of which component is
actually "at fault".
