Originally posted by Ash This to me is not as intuitive as having two e-dials. You can sure get used to the 7D's ergonimics, and hence I say that it's personal preference. I consider good UI to have separate thumb and index finger functions for exposure setting changes without having to take your eyes off the viewfinder. You may be able to do this on your 7D, but I found it considerably more finnicky to do so. Again, personal preference.
hmm, maybe im misunderstanding, so let me reiterate, I CAN without taking my eye off the viewfinder, change the aperture with the rear dial wheel with my thumb and shutter speed with my index finger on the front dial on my 7d. If i want to change ISO, i move my index finger above the front dial and hit the iso button still w/o taking my eye out of the viewfinder.
There is a reason why the wheel and didnt put a dial up at the top of the thumb, but unless you use the 7d and some of its features you wouldnt know that. I didnt and now I use it and its come in handy many a times.
The AF-ON button is there. That button can be modified to be the "half press" of the shutter INSTEAD of it being on the shutter button. Its really nice to do that, so when you seperate the two, you can use your thumb to hit the AF-ON button, that will AF/Track etc and once you take your thumb off it will be set, then you can just press the shutter button and take the pic WITHOUT having to worry about it focusing again.
Sports shooters use this to be able to say track a player get focus and then let the button go and if say a ref passed in front it wont refocus on the ref coming across.
The link says it better than I do
Canon DLC: Article: Back-Button Auto Focus Explained