As we start to use our cameras, one of the first things we all learn is that when using autofocus, you softly press down on the shutter-release button, our camera will get focus and then we press it all the way down to take the photo. For many of us, that is how we use auto-focus and never think twice about it. Back button focusing however, can be an incredibly useful tool for photographers and most cameras today will either have or enable you to assign a button on the back of your camera to focus. But why would you want to do this? What’s the benefit of having a separate button to focus with?
One of the most useful uses of the back button to focus we have found is when wanting to get a more interesting frame, maybe with a lot of negative space and the camera focuses on the sky opposed to the subject. Now of course you can work around this in a number of ways, moving your focus point or just doing the half press on the shutter button and then reframing but the second you take the photo, you have to adjust your frame again. By using the back button, I can get my focus, continue to hold my back button, adjust my frame, take a photo, adjust again, take another photo, over and over again, all without losing focus.
Another really great use of this is when using continuous autofocus. The ability to have your camera continuing to focus is incredibly useful when shooting sports or any fast-moving subject but if each time to go to press the shutter-release button the camera has to focus again, you increase the chance you will miss the focus. By using the back button, you can continuously hold focus even while snapping photos.
Either way, what the back button focusing enables you to do is separate the focusing from the physical act of taking the photo. It gives you time to get focus, adjust your frame, take a photo and still have the same focus without having to focus again. There are many scenarios where back button focusing is superior to the traditional shutter half-press:
- Shooting a portrait with a subject that is only making minor adjustments to their pose between photos. You want to take a rapid succession of shots and don’t want the AF system to choose a different focus point each time.
- Fast-moving action, kids or sports photos, as seen before. Using the back button to focus will help reduce the lag time between half-pressing and fully pressing the shutter button to take the shot.
- Situations where the AF system can get confused with what to focus on. For example, shooting through a busy foreground like a net or a gate, it’s easy for your DSLR to want to focus on that rather than what’s behind it. With back button focus you can choose to keep the focus locked on the background, even if you recompose the photo.
- When you need tack-sharp images. Half-pressing and holding the shutter button to lock focus shifts the weight balance in your hand. Simply pressing the shutter button down fully to take the photo reduces the effect of hand and camera shake in photos.
Depending on your camera model, back button either needs to be turned on in the menus and you then assign the function to a dedicated button, or it is already active by default. Unfortunately, some entry-level models may not have the ability to use back button focus. If in doubt, check the manual. The most important thing you need to know about setting up back button focus: you must turn on the continuous AF mode (AF-C) on your DSLR for it to work on Nikon models. You don’t have to shoot on the equivalent mode on Canon models, called AI Servo, but it will make it easier.