Sure there's noise, but I was making a point about the low light autofocus ability of the center point, to myself (I shot this in January). The 5D3 and 1DX, would not have autofocused at all in this light.
The image was shot at 1/13 s, f/1.8, ISO 25600. That equals -2 EV
, which is within the AF specification for the 5DIII and 1D X. So either you're statement highlighted above is wrong, or you are saying that Canon is lying about the specifications for the 5DIII and 1D X. Which is it?
And of course the bubble level is not razor sharp. But consider the conditions. 1/13 of a second, at a distance of 4 inches, no image stabilization. The point is, the bubble level is in the plane of focus. You can try to deny it, but I'm sorry, it is.
I don't believe that plane of focus passes through the bubble level, although I'll accept that the bubble is within the DoF. As I'm sure you know, the 'plane of focus' is an infinitely thin plane parallel to the image sensor (ignoring field curvature), and the DoF is the region in front of and behind that plane that remains acceptably sharp, defined by a set of arbitraty criteria. With your settings the DoF should be 50/50 in front of and behind the focal plane. Since the index mark behind the bubble is more in focus than the lettering in front of the bubble, the plane of focus is actually behind
the bubble, and the DoF extends forward to include the bubble and backward to include the index mark. That's consistent with the backfocus caused by focus/recompose.
The other point is that the bubble level certainly doesn't appear sharp - nothing in the image really does. That supports my earlier contention - you are at -2 EV, still within the specification of the 5DIII and 1D X for low light AF, and you are struggling to get a usable image at that light level. In half as much light, the 6D could still autofocus…but you can't open up your lens another stop, you'd get more camera shake at 1/6 s, or far worse noise at ISO 51200, and basically have an unusable shot (and it's a stretch to call the existing shot usable). As I stated, the benefit of -3 EV over -2 EV for AF sensitivity is really, really limited in applicability.
In any case, you have almost no experience with the 6D, thus your contributions to this thread are less valid, than those with more experience with the camera.
What does that say about the validity of your statements regarding the 5DIII and 1D X? I think we have an answer to that already, given your inaccurate claim above.