While shooting some portraits recently, there was a discussion about camera controls and different people’s preferences for how they set-up and use their camera. One major subject of discussion was back-button focusing with those who use it being total converts who would never switch back.
So here’s an introduction for those who have never heard of it …
What is Back Button Focusing?
For most cameras pressing the shutter button halfway starts the metering and triggers the auto-focus to focus the camera, with a full press of the shutter button actually taking the picture. With back-button focusing the auto-focus is triggered by a separate button (usually) on the back of the camera.
Why would you want to use Back button focusing?
The main advantage of back-button focusing is that for subjects which are a constant distance from the camera, once you’ve focused (with a single press of the back focusing button), you can then forget about focusing and can concentrate on composing your picture. In this respect it’s just like the way you can select exposure lock to hold a particular exposure setting. You can think of back button focusing as a way to focus lock.
One problem with combining the focus and shutter buttons is that each time you half press the shutter the camera will re-focus – if your subject is directly under a focus point this doesn’t cause any problems, however if your subject has moved away from the focus point or something passes between the camera and subject there is always the danger the camera will re-focus on something else.
The final advantage with back-button focusing is it allows you to switch instantly from Single shot to continuous focusing. By pressing the back focus button once you can achieve single shot focus, by holding the button down the camera will continuously focus.
How do you switch it on?
Firstly you need to make sure your camera offers Back button focus. Back button focus is only available on DSLRs and tends to be on the mid to top range camera bodies; so for example it’s available on Canon’s enthusiast level cameras and above (i.e. those with 1 or 2 digit model numbers, for example the 7D, 70D, 60D, 5D etc.). However, the easiest way to tell is to simply look for a button marked AF-ON.
Secondly you’ll need to configure how the camera uses the different buttons. In most cases you won’t be turning Back-button focusing on (for many cameras the AF-ON button will already be configured to start auto focus) but you’ll be removing focus from the shutter button. The details will depend on your individual camera and you should check your manual, but the general process is as follows;
- Open your camera’s menu
- Within Camera configuration
- Select Custom Controls
You’ll see a list of each different button and what it does
- Select the shutter button (half press)
By default this will be set to AF-ON & Metering start.
- Change this to Metering Start
- Confirm the change by selecting OK.
These examples are for Canon (from a 7D Mk II) but similar options will exist for many cameras.
How do you use it?
Right, now that back button focusing is enabled here’s how to use it.
When you’re ready to take your picture;
- Roughly line-up your camera as normal
- Make-sure you’re focusing point is over your subject (for example on your subject’s eye)
In the example below you can see the focus point is over the subject’s face.
- Press the Back-focus button – The camera will focus on the point you chose.
- Re-compose to your final composition and press the shutter button.
As I’ve re-composed the focus point is now over the background
If you want to take another shot and your subject hasn’t moved simply line up and press the shutter button, there is no need to re-focus.
If you want to take another shot but your subject has moved put the focus point on your subject press the AF-on button, re-compose and then press the shutter button when you’re ready.
Putting it into practise
Now, go out and practise shooting! You will find it strange for the first few hours, however persevere – after a while you’ll never want to go back!
Back button focusing only applies to the creative modes (Manual, Aperture and shutter priority, and Program), if your camera has an Auto or green mode, this will always use shutter button focusing allowing you to quickly reset your camera to normal for less experienced users.