Quote Originally Posted by ThomasJ
Particularly when the image is way out of focus, the AF has a hard time finding it's way - times where the 24-105 is quick in getting there.

At least part of this is probably due to the greater travel of the macro. The non-is is the same: Af is snappy if you're close, but it takes a little longer to find focus from way off... it has a long way to go, after all.