Photography Tips From The Pros: Back-button focusing
Most people focus a lens by pressing the shutter release half-way down, but many cameras offer an alternative approach that pros like to use: the AF button.
As this button is usually found on the back of the camera, the technique is called back-button focusing.
One of the benefits of back-button focusing is that you don’t have to worry how hard you press it, you won’t accidentally take a shot.
It’s also very useful when you’re photographing moving subjects as it allows you to keep them sharp in the frame without locking the exposure settings until you press the shutter release to take the shot.
Back-button focusing is useful when photographing subjects like plants and flowers that move about in the wind.
You can lock the focus with the AF button and fire the image when the composition and lighting are right. It saves time and effort because the camera won’t focus every time the shutter release is pressed.