Back Button Focussing
9th July 2019
A subject often discussed on a Wild Images photography tour is that of focusing and more specifically, how to consistently obtain accurate focus. It is an area of photography that photographers, especially those starting out, often struggle with. Being able to ‘effortlessly’ acquire focus on your subject or scene when in the field is super critical to making sure that your photographs are always sharp where they need to be.
Fortunately for us, many camera manufacturers provide photographers with fully customisable tools of the trade. Todays’ camera systems are jam-packed full of special features, options and modes, aimed squarely at optimising user efficiency.
One such performance enhancement, for many photographers, is a feature called back-button focus. If you are not yet familiar with this technique, then we are here to help. In this article we will be covering back-button focus in detail and highlighting its pros and cons. It might change the way you take pictures in the future!
So, What is Back-Button Focusing?
Back-button focusing is a shooting technique that substitutes the standard default function of the shutter release button – which is to focus (press shutter half way down) and to take a picture (press shutter all the way down) – into two dedicated controls to help you effortlessly lock focus.
In effect, you are taking the autofocus function away from the shutter button and re-assigning it to another button on the back of the camera (which in most cases will be marked AF-ON). Your shutter button is then just that, a shutter for taking the picture!
Why use Back-Button Focusing?
At first, what we have suggested above might sound utterly counterintuitive and you are probably wondering – “why on earth would I want to do that? What is wrong with the way I am currently taking pictures?” and, these are valid questions.
The problem with your camera’s default solution is that if your subject moves out of the plane of focus, you will need to half-depress the shutter release button again to regain focus, or if you are shooting in continuous servo mode, you will need to half-depress the shutter release and hold it there to track your moving subject.
But what if your subject is stationary and all you want is to focus and recompose for a better composition? Certainly, you could switch to One Shot (Canon) / Single Servo – AF-S (Nikon) mode, lock on your subject then focus and recompose, however each time you switch from a stationary to a moving subject, you will need to remember to swap from – One Shot to AI Servo on a Canon or Single Servo (AF-S) to Continuous Servo (AF-C) mode on a Nikon – to be able to continuously track your subject.
Using Back-Button Focus
By moving the focusing function to a dedicated button (usually marked as ‘AF-ON’ or sometimes ‘AE-L’ / ‘AF-L’) on your camera and using the shutter release button only to take pictures, you can streamline the process. Any time you need to focus, refocus or continuously track the subject, you engage the focusing button. If you need to take a picture, you engage the shutter release button. There is no need to remember which focusing mode you are using, because you can always keep your camera in AI Servo / Continuous Servo (AF-C) mode.
Back-button focus allows wildlife photographers to have the best of both worlds. With the AF-ON button pressed and the camera set to AI Servo / AF-C, you can focus on your subject (such as this wonderful Atlantic Puffin) using one of your top right-hand focus points. Once proper focus is acquired, you can let go of the AF-ON button (which prevents further focus acquisition) and recompose the frame so that the puffin is where you want it in the image.
Dealing with Obstructions
Moving subjects will often confuse the autofocus of your camera. Since AI Servo / AF-C is used to track movement, if something gets in the way of the subject the focus system may attempt to lock onto the obstruction. With back-button focus, you can momentarily remove your thumb from the AF-ON button while still taking photos of the subject using the shutter button.
Setting up Back-Button Focus on Your Camera
Depending on which Canon model you are using, the Custom Menu will be laid out a bit differently, but in all recent models the following functions can be found in the Custom Function Menu:
- Open Custom Functions in the Menu
- Scroll to the Custom Controls screen
- In the Custom Controls screen, set the shutter button to “metering start” (which stops the shutter button from engaging focus)
- Set the AF-ON button to “metering and AF start”
If you use a Nikon camera, the process of setting it up for Back-Button focus starts with the Custom Settings Menu. Depending on which Nikon model you use, the Custom settings Menu will be laid out a bit differently, but in all the recent models of higher-end DSLRs, the following settings can be found in the Custom Settings Menu:
- Open the Custom Settings Menu
- Select the “Autofocus” tab
- Select “AF activation”
- Select “AF-ON only”
For Nikon models that don’t have an AF-ON button, you will need to set up the AE-L / AF-L button in the Custom Settings Menu to use it as if it was an AF-ON button:
- Open the Custom Settings Menu
- Select “Controls” tab
- Select “Assign AE-L/AF-L button”
- Scroll through the different options in the menu until you find “AF-ON”
- When on the “AF-ON” option, select “OK”
If you use a Sony SLT or a mirrorless camera, you can also move the focusing button to one of the buttons. If you shoot with the latest cameras like the Sony A9, A7 III or A7R III, there is now a dedicated “AF-ON” button on those cameras that you can use for back-button focus.
- Click on the Menu button which automatically places you in the first Menu tab (colored in red)
- In the first Menu Tab scroll over to screen “AF2” screen
- Scroll down to “AF w/shutter” and set that to “Off”
Since the dedicated focusing button (AF-ON) is only engaged when you need to focus, you can keep your thumb off of it when you need to lock focus and simply keep on shooting. It really is that simple. That said, and like all new skills, back-button focusing does take a little bit of time to master, but it is worth persisting with, because in no time at all this method of taking pictures will become second nature.
Contributor: Andrew Sproule (text and images)
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