The recent EOS 5D Mark III Firmware upgrade 1.2.1 enables the center AF point to autofocus when the combination of a lens and a teleconverter’s maximum aperature is f/8. This means the 5D Mark III will now autofocus at only the center AF point when using the Canon 2X teleconverter with a Canon 500mm f/4 or 300mm f/4 lens.
After installing the firmware update on the Canon 5D Mark III, I tested the new firmware by photographing birds in my backyard. I used the following set up.
Canon 5d Mark III
Canon 500 mm f/4 is
Canon EF 2.0X III Telephoto Extender
Mounted on a sturdy tripod with a gimbal head
The bird photos were taken in the late afternoon just before sunset so the light wasn’t too strong. The birds were roughly 60 – 70 feet away.
The photos were taken in Canon Raw format and were only lightly processed (contrast, shadows lightened). No noise reduction or sharpening were applied to the photos.
Overall, I was happy with the performance of the 2X teleconverter with the Canon 5D Mark III. As expected, some of the photos were softer than without the telephoto extender. I also found that the number of keepers was lower than without using a teleconverter though not significantly more than using the 1.4X teleconverter.