It seems like there are two different explanations on the net for back button focusing: Simply assigning an AF lock/on button for your thumb and disabling the AF at half shutter push. Depending on the camera you either push or hold the button to lock the focus and shoot with out having to reestablish focus. With the GM5 you cannot disable the AF at half push of the shutter. This is fine by me. I like shooting a hybrid way of half pressing to establish focus, then pressing the AF lock (FN 2) to lock in that focus. This is a habit the GF1 taught me. A convenient way of holding the AF/AE button down while the subject is moving (camera is in AFS mode) and having the camera basically AFC on the subject while you snap away. I'm referencing this video where its seems like he is using method 1. when his daughter hits the ball. And when his daughter is running towards him he's holding down the button (damn look at how big that camera is ) and the camera is keeping focus on her while he's shooting away. I'm interested in #2. Is it possible to a varying degree with the GM5?