Larry Weinman wrote in post #18537028
It is my understanding that the 70-200 f2.8 ll is the only series ll lens that does not benefit by the chip in the Canon 2X lll teleconverter. I tried the 2X lll on my 70-200 f2.8 ll and it is a dog as far as AF speed and the AF gets easily confused when focusing near the minimum focus. I have the 100-400ll and that focuses quickly even when the 1.4 is attached.
Fascinating. The 70-200mm II is one lens I have not had a chance to try the MkIII.
TeamSpeed wrote in post #18537031
I am pretty sure the AF improvements are restricted to the long fast primes like Canon EF 300mm f/2.8L IS II USM Lens, Canon EF 400mm f/2.8L IS II USM Lens, Canon EF 500mm f/4L IS II USM Lens and Canon EF 600mm f/4L IS II USM Lens.
When using 5D4 for example, the difference between MkII and MkIII T-cons is substantial in the AF dept. None of Canon's previously imposed mandatory AF slow down "for focus precision" and all points active @ F/8.