It didn’t make sense at first. Use the AE button on the back of the camera for focusing? How is that supposed to be easier and/or better than the traditional method of pressing the shutter halfway down? I mean, that’s what I know, that’s what I’ve grown to know, that’s what’s normal! Is this an elitist purist thing? Or is this real? About a year ago, I decided to truly dig deeper into the idea behind back button focus and, well, like a classic case of neuro-plasticity, over the next 90 days, I had inadvertently rewired my brain to wonder the exact opposite of what I was wondering when I started this little experiment…how did I go this long without it?
The idea is this: Back button focusing basically frees up the shutter button to be, well, a shutter button. Once you wrap your head around that novel idea, the fun part begins. This is the stage when your brain begins the process of peeling the two functions apart from synonymity, realizing that once you have separate control of focusing and firing the shutter, everything becomes clearer (pun intended…sort of).
When you’re using the shutter halfway down method of focusing, each time you move the camera, you have to refocus on your focal point. Unless you’re able to be steady enough to keep that shutter halfway down without clicking the shutter, sometimes for several minutes at a time, this can become a bit tedious as your brain keeps focusing and firing the shutter as a single married entity. But, once you realize they’re a horrible couple and you break them up and see how silly it was that they ever got together to begin with, your brain begins to understand that it should be able to focus on the task of focusing, and then, turn all its energy to the composition of the shot itself.
In other words, once you focus, as long as you stay in that position, you won’t have to focus again. You can expend all your energies on the composition of the shot with the peace of mind that your shots will be sharp from simply setting that focus once, rather than having to refocus with each shot, each press of the shutter.
Essentially, the photographic process goes from:
compose, focus, shoot, re-compose, re-focus, shoot, re-compose again, re-focus again, shoot.
focus, compose, shoot, compose, shoot, compose, shoot.
My brain already hurts less just thinking about it.
Just imagine the decrease in brain strain when shooting at events and weddings and wildlife knowing that your shots are in focus by just having to focus once instead of with each shot! All because once you release the back button, so long as you remain the same distance away from your subject(s), you can re-compose to your heart’s content confident that focus will remain on that plane of field. The amount of ‘keepers’ is bound to drastically increase!
Additionally, this works really well on moving objects such as sports or wildlife. For example, let's say a car was coming towards you, you can focus on the part of the car you want, hold down the back button for focusing, keep it held down and aimed at your chosen focal point, and that point will continually stay in focus. You can then independently fire the shutter while your finger is still holding down the focus button so all of your attention is aimed at the focal point and nothing else, ensuring with better accuracy that you'll get the sharp focal point you want. Conversely, with traditional shutter-halfway-down focusing, once you press down on that shutter, any movement in those milliseconds between auto-focus disengaging and the shutter firing, especially when working with fast moving subjects, and you'll have less of a chance of getting a sharp shot. Once you use it and get used to it, there is no turning back.
Anyhow, most DSLRs and newer mirrorless cameras offer the option - it would be in your settings menus. In most Canon DSLRs, look for the “Metering Start / Meter + AF Start” option in the “Shutter/AE Lock Button” menu. In most Nikon DSLRs, first navigate to the “Custom Settings Menu,” choose “Controls,” then “Assign AE-L/AF-L Button”, then “AF-On.” Now, in the “Custom Settings Menu,” choose “Autofocus,” then in both “AF-C priority Selection” and “AF-S Priority Selection,” choose “Release” so that the shutter will still fire even if if it thinks you didn’t focus because the shutter button wasn’t pressed halfway.
If you have a different kind of camera, Just Google your camera make and model with 'back button focus' and you should be off and running.