How to Set Up Back-Button Focus (And Why So Many Pros Swear by It)
Almost every camera you have ever used works the same way out of the box: press the shutter button halfway to focus, press it all the way to take the photo. One button, two jobs. It is so intuitive that most photographers never question it. You half-press, the camera focuses, you press the rest of the way, the shutter fires. Simple.