Back Button Focus

Back button focus is a technique used in photography that separates the focusing and shutter release functions on a digital camera. Instead of the default setting, where the shutter button is used to both focus and capture an image, with back button focus the user assigns the focusing function to a button on the back of the camera (usually the AF-ON button). This allows the user to focus independently of capturing the image. This can be useful in situations where you want to lock focus and recompose the shot before taking the picture. For example, putting a near object in focus within a wider composition.