I updated the Metabones to firmware v.0.45, and the 70-300L IS does seem to focus a bit better - although it is now also slower.
Just for the sake of curiosity, I tried an old 50mm f1.8 lens (first version, with metal mount, circa 1988), and it actually seems to focus better on the A7R II than it does on my Canon bodies... a very pleasant surprise.
Oct 12, 2015 at 08:57 AM
Previous versions of molson's message #13238606 « A7RII and Canon lenses AF compatibility »
