I discovered a fatal flaw with the 5d iii af system. Using a sigma 150mm macro lens(which the cam probably thought is the 180mm L), only 33 focus point can be used. It is actually pretty ok considering that the other bodies don't even have 33 af points, but the problem is that all the 33 af points are pretty much stuck in the middle, kinda like the outer af point spread on the 5d II. This is crap for af in macro considering that the dof is quite thin for recomposing...Apparently the 100mm macro can have all the outer af points.
Why is this so?