Kenko Pro300 DG Firmware Upgrade - 2 Thumbs Up!
Just got my TC back with the firmware upgrade. No problems whatsoever with the newer Canon lenses. The upgrade makes the 300DG functionally equivalent to the 300DGX. 100L and 70-300L snap right into focus, although a little slower in low light, but not appreciably so.
I'm going to try and stack the DG and DGX and see what happens tomorrow!
Here are some samples straight out-of-camera (70-300L + upgraded DG):
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