01-12-2011, 08:13 AM
I don't know how it is in Canon's but the squares are also a bit larger on the AF sensor than seen in the viewfinder. So if you check the angle of the wall and the nail perpendicular to it, you'll see that the head of the nail seems to be in focus. And the head of the nail is "almost" on the same focal plane with the in-focus wall part. I agree with BC, you'd better test it in another way.
Serkan
Serkan