bcherincoff, I have a question about your 5D III and the Sigma 12-24. Is it the 1st gen 12-24? And if so does the camera communicate with it ok for aperture and autofocus? And the 1st gen has a gel holder on the rear of the lens?
It's the first gen version. Aperture and autofocus worked. It does have a gel holder on the rear. Again, I only tested it with the extender just for the sake of seeing if it worked. Why someone would want to use an extender on a lens that is purposely made for extreme wide angle is beyond me.