I may just be announcing my ignorance here, but I was quite surprised to find that in live view only, my 5d III autofocuses perfectly when mounted to my Sigma 300-800 f5.6 paired with a 2x teleconverter. As soon as I switch back to regular shooting without LV, it hunts continuously without locking AF, which is what I expected in the first place. I was working with a stationary subject and mounted the 2x and switched to LV to zoom in and manually focus as best I could only to find the AF working perfectly, albeit a tad slowly. I would certainly not use such for action subjects.
I don't know if this is a known plus and I've just been living in a box, but if there is anyone else out there using big glass on a Mark III who also didn't know this, this combination is working for me.
I don't know if this is a known plus and I've just been living in a box, but if there is anyone else out there using big glass on a Mark III who also didn't know this, this combination is working for me.
