surprised this hasn't been posted here yet but:http://www.lensrentals.com/blog/2012/07/autofocus-reality-part-3a-canon-lenses
Very interesting results!
Any lens older than the 70-200 2.8 IS II did much worse with phase AF consistency than with liveview AF on both bodies, 5D2 and 5D3, no surprise, already well known and expected.
Regardless of lens age they all did much worse with phase precision than contrast focus precision on the 5D2.
But with a 5D3, all of the new lenses, on that body only, focus much more precisely!
The 70-200 2.8 IS II was sort of in between somewhat better but not like with the newest lenses.
They found that the new 24mm 2.8 IS, 28mm 2.8 IS, 300 2.8 IS II and 70-300mm IS L all focused much more precisely when used with the new 5D3 (and likely 1DX) AF system than on the older 5D2 and that the 70-200 2.8 IS II possibly focused somewhat better (although they were not sure in this case). They said those few lenses actually focused almost as precisely with phase AF as with contrast liveview AF. The old 300 2.8 IS did not.
So apparently the new AF system can hook into some secret stuff with the newest lens designs.
I wonder if that means that third party lenses are not likely to be able to match the same AF precision of the new Canon lenses on the 5D3/1DX, at least not for some time, since they won't have the special whatever it is that makes the new Canon lenses focus extra well with the new AF system.
part 3B (http://www.lensrentals.com/blog/2012/08/autofocus-reality-part-3b-canon-cameras
) has now been added to the part 3A stuff I talked about above.
Basically yeah only the 5D3 and 1DX have the new ultra precision AF unit although the 1D4 isn't that shabby.
7D, as I've long said, has a LOT more in common with the cheaper AF units than the 1 series ones, it's more the xxD just with more points and some more speed added and more options than high quality focusing units and sensor and most updated code
the newest lenses have high precision rotation readers that allow for nice closed loop AF, without both the new high precision readers in lenses and the new high precision detectors (1DX,5D3 and to a lesser extent 1D4) you won't get the ultra precision
i think you also need to use the center point or at least the center column other than very top and bottom points of that.
Nice that I swapped to both 70-300L and 5D3.