On new DSLRs the focus button is paired with the shutter release in a two-stage button; pressing halfway down will activate the focus, and a full press will take the picture. This combination can be fine for most occasions and everyday life events. Separating the focus button from the shutter to a dedicated button on the back of your camera is aptly named back button focus, and has great benefits.
When trying to capture that critical moment having your finger half pressing the shutter is less than ideal and can cause camera shake from your hand cramping. Furthermore, it allows for the ability to set focus with one button, then shoot with the other when the moment is right. If you focus with the shutter release button, say, on a bride, and then someone walks in front of the lens the focus will shift, but you don’t have that issue with back button focusing, and that’s just one reason.
Back button focus makes focus and recomposing simpler, and you don’t have any accidental exposures when in the middle of a recomposition. Using the technique allows you to more easily capture motion in the street, sports or wedding photography with your AF-C (auto focus continuous) mode.
Back button focus can be beneficial to your photography if your camera supports it. I know for Fuji shooters back button focus isn’t implemented in the came way as Canon, Nikon, and Sony; the work around can be a little flaky at times. If you haven’t set up you camera to use back button focus, give it a try. As you begin to use your camera more and more, you may wonder how you have ever lived without it.
Back Button Focus – How To Get Started
Take out your camera’s owner’s manual and look for the section discussing back button focus. Some cameras have a button dedicated to this while others have a button that you can assign to strictly be your focus button. For the majority of users, you’ll need to change the function of the AE-L, AF-L button to be AF on from your camera’s menu. Once you’ve done this, the rest is basically a matter of practice and becoming familiar with the new location of your focus button. (Also, if it intimidates you in the least, I’d recommend checking out our Photography 101 course to get up to speed and snapping away in no time!)
The only way to become accustomed to this is to spend time using it. When I initially began using back button focus, I would spend time while watching TV or hanging out in the backyard framing shots and using the new focusing format. You could also plan a photo shoot or specific period of time where you know you aren’t going to use the half-press shutter method or go out and take some street photos utilizing the back button method only. I’ve found that as I’ve become more comfortable, I tend to use it more and more as I like having the increased level of control I feel it gives me.
You’ll find that as you use it more, you’ll either wonder how you survived this long without it or wonder what the hype is all about and go back to the default method. For me, it’s very beneficial. I’m able to focus on my subject with less contemplation of which of the myriad of focus points to choose from, less worry about accidentally snapping a worthless photo,  or missing focus because my subject moved just a bit and ended up  with a less than ideally sharp image.