I discovered this last night, I'm very disappointed, I havent tried my kenko extension tubes yet, i'll try them later and see. I hope canon fix this with a firmware updateMy Kenko 1.4x & 2x TC work fine with my 5D3. Use it with the 70-200 f/2.8L.
Can you confirm which ASIN number is on the TC that you have working. Do other lens work? Which AF point do you use ie, center, right of center, left of center, up from center. I have read that some focusing points work better then others.
I want to use 2x with future 5d Mark III with EC 300mm f74/l to gain the extra crop (length) for bird photography. I have used kendo 2x DGX with 7D and 300mm f/4 and worked great.
Thanks for your feedback.