你的說明與D200的並無差異啊, dpreview是這樣寫的: AF-ON button (repeated on the vertical hand grip) is an alternative to half-pressing the shutter release, it triggers the camera's auto focus system. You can if you wish have the camera set to that AF is not triggered by a shutter release half-press (CSM a5) and only by the AF-ON button (some photographers prefer this).