Teachable Moment - Back Button Focus in DSLR Photography

Why is back button focus such a mystery to some while others swear by it? Let’s have a look... 

By default, the shutter release button also activates the Auto Focus; when you half press the shutter button the AF starts to look for something to lock on to. This way of focussing has become so intuitive that we barely notice it but using this approach to AF can become a problem in some situations.

If something moves in front of your subject when you’re about to fully press the shutter button to take your photo the AF can suddenly latch-on to the wrong thing. In wildlife photography this could be long grass moving in front of an animal or if you’re photographing something like a busy event a person might walk past between you and your subject. Missing a great moment like this can be really frustrating.

Thanks to missing my focus, here’s a nice photo of some grass with a cheetah in the background.

Thanks to missing my focus, here’s a nice photo of some grass with a cheetah in the background.

Back Button Focus removes the AF function from the shutter button and assigns AF to a button on the back of the camera which you can press with thumb of your right hand (check your manual to find out where this button is for your camera). This frees the shutter button to only operate the shutter. Using the back button, you can find focus and then release the AF button, effectively locking focus a fixed distance from the camera. Now there’s no chance that the AF can trip you up if something moves in front of you just as you are about to take the shot.

A better result - once I focussed past the grass in the foreground I was able to take my thumb off the back button to effectively lock the focus and then release the shutter

A better result - once I focussed past the grass in the foreground I was able to take my thumb off the back button to effectively lock the focus and then release the shutter

If the subject itself moves in the time between focusing and taking the photo you can simply press the back button to find focus again and don’t forget, you can also keep your thumb on the back button to continuously track the focus.

In the situation below, using traditional focussing (half-pressing the shutter button to activate AF) the camera would struggle to find focus on the leopard. It’s much more efficient with back button focussing; a few taps of the back button to find focus, release the button and shoot.

The key here, as with a lot of camera craft, is to set your equipment up to work for you and not against you. Back button focussing does this effectively. It does take a little bit of getting used to you but try it for 30 minutes next time you’re out with the camera and I’m sure you’ll see the value of this approach. 

Good subjects for back button focussing:

  • Wildlife

  • Weddings / Event coverage

  • Portraits

  • Sport


Do you use back button focus or have you never seen the point? Let mw know what you think in the comments and please share this if you found it helpful. 

GD.