Sometimes of course it infuriatingly locks onto the background, but I had the impression that once focus lock was achieved it kept it well even when the subject was closing like a bat out of hell (hey that’s a good title for a song!). I have to temper this by saying however that you cannot just expect to get results from the MK3 out of the box as the autofocus will need some customization to get the optimum results. So far though so good and I am finding that the Mk3 is a fun camera to use as I trying things that I would never have previously.