Back button focus is just what it sounds like. Instead of using a half-press of the shutter button to activate autofocus, you hold down a dedicated button on the back of your camera instead. When you let go, the focus stays locked. Here’s why you might want to use it.
RELATED: How to Get the Most from Autofocus With Your Camera
The Advantages of Back Button Focus
The big advantage of back button focus is that it separates the act of focusing from taking photos. The default camera setup where the shutter button controls both actions makes certain things awkward, like trying to focus on a part of the scene that doesn’t fall nicely under an autofocus point. It can also slow down your camera’s burst mode while the autofocus hunts, stopping you from taking pictures.
With back button autofocus, you’re able to focus easily on any subject you want in the scene and then recompose your shot without having to worry about using any sort of AF-lock. And since your focus will stay locked until you change it, you can keep shooting without worrying about autofocus trying to refocus on something else. This is super handy when your subject isn’t moving too much.
Another nice feature is that you don’t have to choose between manual focus or single and continuous autofocus modes. If you enable back button focus and set your camera to continuous autofocus:
- To manually focus, don’t press the focus button, but manually focus using the lens rings instead. Most prosumer and professional lenses will let you manually focus even if the lens is set to autofocus.
- To single focus, hold the focus button down until focus acquires a lock. Then release it and shoot away.
- To continuously focus, hold the focus button down and keep shooting.
As you can imagine, once you’ve got the hang of things, this makes it much faster for you to react to different situations. And as I’ve said time and time again, it’s not about not using your camera’s automatic features; it’s about using them in such a way that you control how they work. Back button autofocus is one of those ways.
Setting Up Back Button Focus
To set up back button focus, you’ll need to dig into your camera’s menus. You’ll normally need to do two things:
- Remove autofocus from the shutter button.
- Set the AF-ON button—or if your camera doesn’t have one, the AE-L (* on Canon cameras)—to activate autofocus.
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Source : What is Back Button Focus?
