MODERN CANON AF: Holy Mackeral!
Just tested the 5D4 with 500mm MKII with both Extender 2X MkIII, and MkII
OMG OMG OMG!!!!
This camera has managed a SIGNIFICANT leap ahead of any previous EOS AF system I have used! Now I understand what they've been talking about in the 1DX2 thread.
With either one of the 2X extenders, didn't seem to matter which, the AF speed, accuracy, jumping from near to far, was like a bare lens on most cameras!
2XIII allowed me to select a huge number of AF points (all?)
2X II allowed selection of any of the 9 center AF points (7 across center, 3 up and down center)
With that limitation vs. the MkIII, I was otherwise unable to see any difference in speed or hit rate.
Previously I had pretty much poopooed the claims that the 2XIII was big improvement for AF vs. the 2X MkII. Maybe I had the wrong camera, or maybe those making the claim had not tried the 2X II on their newer bodies?
What I will say is this, with a fully modern high end body like the 5D4, both the 2X III and 2X II paired with the EF 500mm f/4L IS MKII are performing like nothing I have ever before seen. Super fast AF, jumping from distant to near targets almost like a bare lens!
I immediately had to retry the combo with 7D2 and 1D4, which I have used the same lens/TCon combo on before (as well as 5D3 now sold) . none of which are coming in even CLOSE to being as superbly fast and accurate. The 7D2 is out there in the exact same (superb crisp) light, and it's hunting and not moving from near to far quickly at all.
It appears that the "built in brake" that the Canon 2X converters have always applied to previous bodies, does not engage on the 5D4 at all. It appears to try to AF at full speed, like a bare lens, and it also appears to be successful!
Sorry folks, if your shooting anything other than a 5D4 (or I assume 1Dx2) right now, you are dealing with a very different AF system.
IMHO, this is the biggest jump in actual AF performance since the 1DMkII. None of the other systems in between have displayed such an obvious side by side improvement.
The 7D2 improvements in use compared to 1D4/1D3/1D2 is NOT NEARLY as notable as compared to the 5D4 vs. 7D2!
As of today, I will have to change my stock answer to the age old "should I get a 2X T-Con?" question. Now the answer will have to begin with "shooting a 5D4? Then yes, if not,. well..."