In this second article in this series, I am discussing perhaps the most significant change I have made to my technique since taking up photography. It is the change that has provided the biggest benefit to me, especially for my wildlife photography. That technique is Back-button Focus (BBF).
The Auto-focus systems on cameras these days are amazing, but they can be even more so if you take full control of them.
Please note that I am a Canon user, so what I describe in this article may be slightly biased towards my gear, but I’m confident that the behaviours of most brands are very similar. Like last month’s article, I am not going to delve into how to set-up BBF on your camera, there will be many articles or YouTube videos for your camera if you search the internet.
The default behaviour of most cameras is that when you depress the shutter button half-way the camera meters the scene to set the exposure and initiates the auto-focus system, then when you fully press the shutter, the camera takes a photo. With BBF (in the way I have it set up), the auto-focus function is removed from the shutter button and re-assigned to another button on the back of the camera, effectively separating the exposure metering and taking of the photo from the auto-focus action.
This back-button is then used with your thumb to focus the camera.
This may sound like it is complicating things, and it is somewhat, and it does take some getting used to, but it gives you much more control over the focussing system of your camera, which is especially useful when photographing fast-moving subjects, or changing scenes like wildlife or sports.
Before we discuss the advantages of BBF it is important to understand the difference between the different auto focus modes available in most cameras.
The first focus mode is One-Shot (aka Single-Shot or AF-S). In One-Shot mode once the Auto-focus system is initiated and the camera focusses on something, the focus is locked until you take a photo. One-Shot is designed to be used for stationary subjects. It also allows what is called “Focus and Recompose” where you focus on something, then slightly move your camera to recompose the scene. Also, in One-Shot mode the camera will not allow you to take a photo until the camera has found something to focus on.
The second focus mode is Continuous (aka AI-Servo, Continuous-Servo or AF-C). With Continuous focus mode the camera continues to focus while you have the shutter button half-depressed (or the assigned back-button pressed if using BBF). This allows the continuous focus-tracking of moving subjects.
There are also different ways in most cameras to use the focus points in your camera, you can use spot focus (where you use a single focus point which you can move around the scene), you can use clusters of focus points (in various configurations), and in more modern cameras you even have advanced functions like face or eye-tracking where the camera searches for and tracks the faces or eyes of subjects).
Changing the focus mode, or the focus points settings, through the menu system, or via the back screen, are not things that you can quickly do while engaged in shooting, but BBF allows you to do things much more quickly.
With my BBF settings, I have the camera permanently set to AI-Servo (Continuous) mode. While I hold down the back-button it will act like Continuous, but by lifting my thumb from the BBF button the camera will stop focusing just like One-Shot.
It's nice never having to worry about whether the camera is in the right focus mode.
I have assigned two buttons for BBF, one uses Spot Focus (a single focus point), and one activates Eye-Focus, so I can easily switch between these two favourite focus point settings simply by choosing a different button with my thumb.
It's nice not having to delve into the settings screens to change between my favourite focus point settings.
Figure 1 - My Back-button Focus set-up
One disadvantage of the default shutter button setup is that the camera will try to focus for every single image you take, and this is not always desirable. With BBF you can focus the camera with the back-button, then take as many images as you like without the camera refocussing simply by lifting your thumb off the back-button.
One example where this quickly becomes obvious is “focus and recompose”. Let’s pretend we are shooting a landscape, with a small building that we want to be the point of focus. With the traditional shutter-button focus we can focus on the hut once, and take a photo, but then if I want to try a few more different compositions (by changing the direction of the camera, or zooming in or out) I would need to be careful to move the focus point onto the hut for every subsequent shot, or keep moving it back to the hut and focus and recompose. With BBF, I can focus on the hut once, then take as many different shots as I like with my thumb lifted off the back-button, and the focus will remain the same until I choose otherwise by pressing the back-button again.
Another example is when you want to use manual focus by twisting the focus barrel on the lens, rather than auto-focus. If you were using default shutter-focus, you would need to set the manual switch on the lens to “Manual” (or on some cameras set the camera to manual focus in the menu), to stop the camera focussing each time you press the shutter. When using BBF this is not necessary as you can achieve the same result by simply keeping your thumb off the back-button.
It's nice not having to worry about the Auto/Manual switch on the lens any more.
Essentially though, the biggest difference with BBF is that it just gives you much more control and enables you to effectively use your auto-focus system options quickly when you most need to be changing things on-the-fly.
One of my favourite genres of photography is wildlife, primarily birds. BBF is perfect for this type of photography where the subjects can be sitting still one minute or flitting around from branch to branch then launching themselves skywards. Switching to manual focus when trying to focus through branches becomes so much easier with BBF.
One of my favourite genres of photography is wildlife, primarily birds. BBF is perfect for this type of photography where the subjects can be sitting still one minute or flitting around from branch to branch then launching themselves skywards. Switching to manual focus when trying to focus through branches becomes so much easier with BBF.
BBF will take you some time to get used to, so it probably requires a few weeks of practise time, but once you’re used to it, I think you’ll find it will completely change your photography for the better.
Fig 2 - Back-button Focus works well for wildlife photography
This article was first published in the August 2024 issue of Artists Down Under magazine.