Benefits
Combined Focus Modes – Utilize AF-S and AF-C
The biggest benefit of back button focus, in my opinion, is the ability to combine focus modes. With focus mapped to the shutter button, the photographer must select manual focus, continuous focus, or single-shot focus. Reacting to a scene while attempting to change focus mode is almost impossible, and different focus modes are better suited for different situations. Single-shot focus modes are great for a static subject, such as wildlife standing still, manual focus can work well too. Continuous focus modes are essential when wildlife is moving, the focus will track and adjust.
When focus is coupled with the shutter button, only the chose focus mode will work. The huge benefit of back button focus is you can utilize every mode.
For single focus mode or one-shot focus, simply tap the AF-ON button. The camera will achieve focus and then you can release the button, with focus being unchanged. A bonus of this setup is being able to easily recompose while not having to worry about re-acquiring focus. If focus is mapped to the shutter and you recompose, you will have to re-acquire focus, which takes time and can be the difference between getting the shot and not. It is also just much easier to focus and move your camera around for different compositions.
For continuous focus, just hold down the AF-ON button and the camera will maintain tracking and focusing until you release the button. Simple, right? And for manual focus, you can rotate the focus dial on the lens at any time.
Shutter Button Priority is Changed From Focusing to Taking An Exposure
By default, when the shutter button is pressed the camera prioritizes achieving focus before the shutter release kicks in and an exposure is recorded. That ensures focus is acquired but also means there’s a delay in the shutter release. All of us know that every split second matters for wildlife photography, as they can be the difference between capturing a moment or missing it.
When focus is mapped to AF-ON, the shutter button changes its priority to only triggering the shutter release to take an exposure. This benefit mainly shines through when having to recompose. Think about this scenario – you’re photographing a brown bear, the bear isn’t moving, but you move your camera to re-align your composition that puts the bear in a different area of the frame.
With focus mapped to the shutter button, you will have to depress the shutter halfway to initially take an exposure of the bear, then when you recompose, you will have to once again press the shutter halfway to re-focus before taking more exposures. That process takes time.
Using back button focus, you can press AF-ON once to focus and when you release the button, focus is locked and will not change until you engage the button once again. Thus, you can recompose as much as you’d like without having to reacquire focus. If you tried to do that without back button focus, the camera would re-acquire focus every time you recomposed and pressed the shutter halfway down. It doesn’t seem like it makes that much difference on paper, but it saves time and is much more efficient.
Set Up Your Camera
Every camera system has a different set of menu options, but below you can find general instructions for setting up back button focus with various camera manufacturers. If you haven’t tried back button focus before, I highly recommend it. You will benefit from the switch and notice that your focusing in the field is much more efficient. I haven’t gone back since switching to back button focus years ago, it has been a lifesaver in certain situations.
Nikon
Navigate to the ‘Autofocus’ custom settings menu
Scroll down to “AF Activation” and select it. Choose ‘AF-ON Only’
If your camera does not have a dedicated AF-On button – open the Controls custom settings menu and go to the “Assign AE-L/AF-L Button” option – choose “AF-On”
Change focus mode to ‘AF-C’
Canon
Navigate to the “Custom Controls” or the “C.Fn” option in the menu. These options may be slightly different for each camera model
Choose the “Shutter button/Metering and AF Start” option and change it to “Metering Start”, this removes AF from the shutter release
Back in “Custom Controls”, set the AF-ON button to “Metering + AF Start” – this will turn on the Back Button Focus option
Change focus mode to ‘AI Servo’
Sony
Navigate to “Custom Settings”.
Locate “AF w/Shutter” and turn this to OFF.
Set the AE-L Button to AF-On.
Change camera to continuous focus mode.
Fujifilm
Set the focus selection to Manual
Open your Menu and select AF/MF
Select Instant AF Setting and set this to AF-C
Open the Menu and select Set Up. Choose Button/Dial Setting
Select AE-L/AF-L Button Setting and set this to AF-L/AE-L
Panasonic
Set AF/AE LOCK to AF-C
Open the Custom Setup menu
Select AF/AE Lock and set to AF-On
Select Shutter AF and set to OFF