As RA Baker says you need to press the OK button having selected AF-on only, not the OK in the centre of the 4way selector. Master the idea of using the AF on button to focus and it gives you the advantage of 3 different modes. Set the selector in the lens mount to C and leave it there and you get 1. press and release to focus (single) 2. press and hold to get continuous focus 3. do nothing and get manual focus. It takes a bit of practice to get used to doing the two button presses to take the picture, but I have found it much better since I don't have to think about changing a fiddly switch to alter the type of focus available. the best advice, as with all things is "try it" if you find you can't get on with it or it is not for you, nothing lost - the beauty of digital, it doesn't cost to experiment, no "wasted" film exposures, just deleted files.