Archibald wrote in post #17667594
That would be interesting. I have done informal tests with the Canon 1.4x and they are inconclusive. Would appreciate your findings.
I did a very quick test this afternoon (I had only one hour before sunset). The results with the Kenko 1.4x really surprised me.
Used with the 100-400II lens on the 70D and the 6D the Kenko TC allowed very quick and reliable AF. I tested it at F8 and F9. What was surprising was that AF allowed the use not only of the center point, but also the zones! I have not uploaded the photos on the computer yet, just checked them on the back LCD, but they looked sharp at any magnification.
Then another surprise: I mounted in on the brand new 7D Mk II. The message on the back LCD said that it required lens firmware upgrade, and that it did not find the firmware update on the card. I have no idea how to go about that!
I also tried the Kenko TC with the 70-200 f/4 IS, and it did both zone and single point AF even at small apertures (e.g., f9). However, the camera kept writing images on the card forever, so I had to remove the battery to reset the camera.
All in all, I loved the 100-400 with this Kenko, but I would appreciate any suggestion as to how to update the firmware.