Quote Originally Posted by neuroanatomist
fewer tests would be needed for an f/2.8 or faster lens due to the higher precision.

But isn't the margin for error lower on a fast lens?


Quote Originally Posted by Daniel Browning
The high precision f/2.8
autofocus sensor can only look at the world through an f/2.8 tube. If
there is an f/5.6 hole in the wall, AF wont work. If the hole is
expanded to f/2.8, then it will have an unobstructed view and work
normally. If the hole is expanded to f/1.0, it makes no difference
because the view is restricted by the f/2.8 tube.

This is my understanding is well. With respect to Chuck, I don't believe him.