Do you ever miss shots because the subject is moving and you can’t react and focus fast enough?
Back button focus may help you overcome this problem. It certainly changed the way I shoot.
Using the back button to auto focus gives me the ability to photograph focus quickly on fast moving subjects, track my focus while the subject is moving, react quicker, and overall get a higher percentage of sharp, focused images.
When I first got into digital photography back in 2005, I stumbled upon this term, “back-button focusing”. After reading about how most sports photographers and some wedding photographers use it, I gave it a try. It felt a bit awkward at first, but I stuck with for about a week because I quickly noticed the potential benefits of using it.
Guess what? I still use it, and I haven’t gone back to pressing the shutter half way down to focus method.
What is back button auto focusing?
Back button autofocus is a custom function in your camera where you can separate the shutter button from your focus button. This setup disables the focusing function on the shutter button, and allows you to use a button on the back of your camera called, AF-ON button, for autofocusing.
Once you activate this custom function, the shutter button and the AF-ON button will work independently. The shutter button will be a full-time shutter button, and you’ll be using the AF-ON button on the back of your camera with your thumb to autofocus.
What is the benefit of using back button auto focusing?
The biggest advantage of using this technique in my opinion is not having to constantly press the shutter half way to refocus on your subject before taking pictures. This standard method works fine but it has its limitations when it comes to trying to focus and take multiple shots of moving subjects.
By using the AF-ON back button you can focus on your subject once, let go of your thumb, and use the shutter button to take as many photos as you’d like. Your focus will stay locked in and those photos will all be in focus as long as your subject stays within the same plane.
You may also use the back focus button to lock in your focus and composition and wait until the moment is right to press the shutter.
That’s how I took this photo during a recent engagement shoot. My client was repeatedly giving her dog a treat pretty much from the same spot, so I locked in my focus on the dog with the back button first. I wanted a picture of the dog in mid-air so while holding my composition, I waited until the dog was jumping up the pressed the shutter to fire off a few shots in continuous mode.
Another advantage is, if your subject decides to move away, you can simply use the back button to keep tracking and focusing on your moving subject, while continually photographing with your shutter button. Both buttons work even when you press them both at the same time.
How to setup the back button function
Canon Digital Learning Center listed some of the back button setup Custom Function(C.Fn) menu settings for their cameras that I copied below.
EOS Rebel T3: C.Fn 7 (option 1 or 3)
EOS Rebel T3i: C.Fn 9 (option 1 or 3)
EOS Rebel T4i: C.Fn 6 (option 1 or 3)
EOS 60D: C.Fn IV-1 (option 1, 2, 3, or 4)
EOS 7D: C.Fn IV-1 (Custom Controls — Shutter, AF-ON, AEL buttons)
EOS 6D: C.Fn III-5 (Custom Controls — Shutter, AF-ON, AEL buttons)
EOS 5D Mark II: C.Fn IV-1 (option 2 or 3)
EOS 5D Mark III: C.Fn menu screen 2 (Custom Controls — Shutter, AF-ON, AEL buttons)
EOS-1D X: C.Fn menu screen 5 (Custom Controls — Shutter, AF-ON, AEL buttons)
If anyone has an older Canon camera like the 20D or the original 5D, the custom function setting for both of those cameras are: C.Fn 4 Shutter/AE lock button(option 1: AE lock/AF)
While many of the newer camera models now have the AF-ON button, I started with a Canon 20D and a 5D where this back button function was assigned to the button with the asterisk. And even though I use a 5D Mark II which has an AF-ON button, I still customize my setup to use the asterisk button because that’s what I’m used to. The extra 0.5 centimeter to the AF-ON button feels too far.
To use the asterisk button on the 5D Mark II: C.Fn IV-1 (option 2 or 3), and C.Fn IV-2 (option 1: Enable)
Nikon users, here’s your setup. Every camera may vary but here’s a general step.
If your camera has an AF-ON button on the back of your camera:
Switch the focus mode to AF-C(auto focus continuous mode), go to Custom Setting Menu -> Autofocus -> AF activation -> AF-ON only ok.
If your camera does not have an AF-ON button on the back of your camera, the AE-L/AF-L button is the one you’ll use as the back focus button:
Switch the focus mode to AF-C, then Custom Setting Menu -> Controls -> Assign AE-L/AF-L button -> AF-ON ok.
Here’s a video by Steve Perry who thoroughly explains the Nikon setup(Jump to the 6:54 mark) and its functions way better than I can. If your Nikon camera is one of the models that does not have a dedicated AF-ON button(Jump to the 8:20 mark on the video).
Adopting a new technique takes practice, and it’ll take some getting used to. If you only pull out the camera once in a while, this may confuse you and it may not be worth learning this technique. But if this intrigues you, give it a try.