ricleo
Senior Member
Tony Northrup have tested a few lenses and finds anything more than 300mm AF will hunt. Best bet is Metabone and EF70-200mm maxed.
https://www.youtube.com/watch?v=C1kI4NacaUw
the 70-300L will AF perfectly at 300mm too. I noticed a different limitation to canon lens AF on the sony cameras. the AF is less reliable when you are at or very close to minimum focus distance. very accurate at distances away from MFD, and super good at long range.
at MFD, the lens will usually focus back and forth a few times before getting the focus. I find it also helps if you manually focus to nearly the correct focus for close ups near MFD, and the lens will snap into focus and lock.
this is my experience with the 70-300L and sigma 50 1.4 art