“Er, where do I go now…?!”
Back button focus (or BBF) is an important tool in wildlife, sport and any other kind of action photography.
Normally, you have to choose between AF-S (or Single shot) mode and AF-C (Continuous) mode, which Canon calls One Shot and AI Servo (Artificial Intelligence Servo). AF-S/One Shot works better for stationary subjects whereas AF-C/AI Servo works better for moving subjects.
Some cameras have an AF-A (Automatic) mode that tries to switch from AF-S to AF-C when the camera ‘thinks’ you’re shooting a moving object, but it might get it wrong, which means you might miss the shot!
A better way is to use Continuous/Burst shooting mode and AF-C/AI Servo all the time and set up back button focusing so that you control the autofocus with the AF-ON button (if there is one) rather than by half-pressing the shutter release.
Note that this can be done with any button on the top right-hand corner of your camera that you can reach with your right thumb. It may be labelled AF-L (Automatic Focus - Lock) or AE-L (Automatic Exposure - Lock) or both.
Benefits
Once you get used to it, there are several advantages to using BBF with AF-C in continuous shooting mode:
Ability to focus and recompose. If you have a DSLR, you can’t use autofocus outside the central area where the focus points are. BBF allows you to use one of those focus points to focus on your subject. Once you lift your thumb off the back button, the focus is locked, so you can then recompose your shot. As long as you and your subject don’t move, the image will remain in focus.
Convenience. You don’t have to switch from one focus mode (AF-S) to another (AF-C) when you switch from a stationary to a moving subject or when your subject suddenly starts to move.
Precision. If you’re taking a burst of shots but you have to half-press the shutter to activate the autofocus, then the camera may lock focus as soon as the button is fully pressed. That means the camera will lose its focus on a moving subject after the first couple of shots. (This varies between camera models and settings, so you’ll have to check it in your user manual!)
Reliability. We all make mistakes in the heat of the moment, and it’s very easy to press the shutter too firmly or too gently to activate the autofocus, leading to unwanted shots or a failure to focus. However, the AF-ON button has only two settings: it’s either pressed or it’s not. That means you can press it as hard as you like!
Disadvantages
Just to set your expectations, it should be said that using BBF doesn’t actually improve the autofocus. The camera won’t acquire focus any faster or more reliably than if you half-pressed the shutter.
It’s also true that you don’t need to focus and recompose with mirrorless cameras. That negates the main benefit of BBF. I used to own DSLRs, so I still use BBF, but that’s just because old habits die hard!
Aside from those caveats, there’s only one real disadvantage of using BBF, which is that you have to use your right thumb to focus all the time. That means you can’t use it to do anything else, such as press a function button or move the focus point with the nubbin/joystick. This is not a big deal, but it’s worth bearing in mind.
Set-up
How you set up back button focus depends on your camera. I have a Nikon D850, and it’s very simple:
Press the Menu button
Select the Custom Setting Menu (the one with the pencil icon)
Select a Autofocus
Select a8 AF activation
Switch from Shutter/AF-ON to AF-ON only
Press OK to confirm
On my D810, it’s almost the same except the AF activation setting is a4 rather than a8.
On other Nikon cameras, you might have to go to f Controls and select Assign AE-L/AF-L button.
Canon cameras have a slightly different process:
Press the Menu button
Choose the Custom Controls or C.Fn option
Remove the AF option from the Shutter Release button
Set the AF-ON button to Metering + AF Start
If you own a Nikon, I also recommend two further settings:
Set the drive mode to Continuous High by pressing the release mode dial lock release and turning the release mode dial to Cᴴ
Use the 3D version of AF-C:
Press and hold the AF-mode button (next to the lens release button)
Turn the main command dial (on the back of the camera body) to select AF-C
Turn the sub-command dial (on the front of the camera body) to select 3D
Usage
There are three different ways in which you can use back button focus:
Press once
Press and hold
Don’t press at all
Press once
This method is used to ‘focus and recompose’. It’s useful when you’re taking pictures of a static subject, but you want to try out different compositions, say with the subject in the top left corner or in the bottom right corner.
All you need to do is follow a few simple steps:
Move the focus point until it’s over the eye of your subject
Press the AF-ON button once
Move the camera so that your composition is the way you like it
Press the shutter
If you want to take a number of different shots with different compositions, you can forget about the AF-ON button. Once you’ve pressed it, the focus is locked, which means all you need to do is concentrate on framing the shots and taking pictures.
This is particularly useful when you want the focus point to be outside the central area in the viewfinder. There’s just no way to move it to the edge, so all you can do is focus and recompose.
Most modern cameras allow you to move the focus point around in the viewfinder, and if you’re taking a series of shots of an impala in profile, say, it’s much easier if you simply move the focus point over its eye (obeying the rule of thirds) and keep it there.
It’s a useful skill to be able to do that while you’re shooting, and that’s easy enough to do on the D850 by operating the sub-selector ‘nubbin’ or the multi selector with your right thumb.
However, there’s no DSLR on earth that allows you to move it wherever you like in the frame, and that’s where focus and recompose using back button focus comes in.
Press and hold
This method is generally used to shoot a moving subject, but you can also use it for ‘static’ subjects. The reason I put that in inverted commas is because subjects are never truly static - especially wildlife!
Animals and birds are constantly twitching, blinking or looking from side-to-side, so taking a burst of two or three shots in AF-C/AI Servo mode is advisable even if all you’re looking for is a simple portrait.
Here is what you need to do:
Frame your composition
Move the focus point until it’s over the eye of your subject
Press and hold the AF-ON button
Pan across to follow your subject (if it’s moving)
Press and hold the shutter
This is only a brief guide to using back button focus, and there’s a lot more to taking great pictures of birds in flight, for example, but feel free to check out my article on that after you’ve finished this one.
Don’t press at all
This sounds a bit daft. Why would you go to all the trouble of setting up back button focus and then not even use it?!
Well, the answer is that not pressing it is the same as using manual focus.
There are many occasions when you might want to switch off the autofocus, and this is the easiest method of the lot.
You don’t have to fiddle around with the AF-mode button or worry about whether you’re in manual focus mode or not.
Effectively, you’re always in manual focus mode as long as you don’t press the AF-ON button.
Here is what you need to do:
Nothing at all!
Conclusion
I hope that gives you enough evidence to want to try out back button focus for yourself.
It’s a great tool, and I use it all the time for my wildlife shots.
The only objections to it are that other people might not know how to use it if they borrow your camera and it means you have to do two things with your right thumb: move the focus point and press the AF-ON button.
If you can cope with all that, then you’re good to go!
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