Photo Safari Skills: An alternative to Back-button Focus

29th July 2016

Ever since auto-focus appeared on cameras, photographers have used the shutter button to focus, meter and take the final shot - half-press to focus & meter, and full-press to take the shot. When you half-pressed the shutter button, the camera's focusing system would behave in one of two ways:

  • if you had AF-S (Nikon) or ONE SHOT (Canon) selected, the camera would achieve focus using your selected focus point(s) and then hold that focus until you took the shot, or released and started again.
  • if you had AF-C or AI SERVO selected, the camera would acquire focus, and continually re-acquire focus until you fully-pressed the shutter and took the shot.

AF-C / ONE SHOT was good for portraits and static subjects, and AF-C / AI SERVO was good for moving subjects. The former was also most useful for focus-and-recompose photography, perhaps when you wanted to place your subject at a point in the frame where there was no convenient focusing point.

Wildlife photographers wanted to have both options available all the time - they wanted to be able to track movement as it occurred, but then be able to focus-and-recompose if the subject stopped moving. Switching between the AF-S / ONE SHOT and AF-C / AI SERVO modes was time-consuming and tiresome, especially in a high-speed situation.

So a few years ago, the phrase "back-button focus" appeared in the world of wildlife photography. This is how it works: you set up your camera to use the AF-ON button to focus, and the shutter button to meter and take the shot. This means you can have AF-C / AI SERVO performance when you hold your thumb down on the AF-ON button, but if you lift if off, you can still take shots (using the shutter) without the camera re-focusing. It was a great idea.

Imagine an example: as a lionness walks towards you, you hold AF-ON with your thumb and take lots of shots using your finger on the shutter. When she stops, you focus on her eye using the AF-ON button under your thumb, then lift your thumb, re-compose, and take shots with her placed elsewhere in your frame. No need to switch to AF-S / ONE SHOT mode.


By using the customisation functions in your camera's menus, you can set up the camera to focus only when the AF-ON button (shown here on Canon and Nikon cameras) is pressed down. This allows the photographer to have AI SERVO and ONE SHOT focus capabilities without having to change mode.

However, to me there were always several problems with this arrangement:

  • I use my thumb to move the chosen focus point around in the frame which is tricky if I've got it held down on AF-ON.
  • I want AI SERVO performance most of the time, so I have to keep my thumb on the AF-ON button for long periods, which I find tiresome.
  • It is tricky to learn a new style of photographing after many years, and you risk missing shots until you've mastered the new technique.
  • If someone else picks up your camera they won't successfully take a photo unless they know to push the AF-ON button to focus.

While looking through the camera's settings, I found a solution to the same problem that I find much more intuitive. Instead of using the AF-ON button to focus, I use it to STOP focus.

While that lionness is approaching me, I use the shutter to focus, meter and take photos, while re-positioning the chosen focus point using my thumb. When the lionness comes to a stop, I can focus using the shutter button (half press) then hold my thumb on the AF-ON button to lock focus, re-compose and shoot my image. I think this option has several distinct advantages:

  • there is no need to re-learn how to focus with your camera
  • you only need push the AF-ON button when you want to focus-and-recompose
  • your thumb is free to move the focus point around in the frame
  • anyone can use your camera, because it performs as they expect it to!

So, I must admit that I do not use back-button focus! Or at least, not as many others do. If you are interested in the idea, and haven't yet made the switch, try setting the AF-ON button as an AF-STOP capability and see how you get on. If you are a BBF user, but struggle with it (as I did) then maybe give my alternative a try!

Comments

Photo comment By Dave Pressland: This is a good tip and I much prefer it to using back-button focusing. However, on the Nikon camera pictured, immediately to the left of the AF-ON button circled is a button marked AE-L/AF-L which under default settings does exactly what you're suggesting, plus it locks the exposure too. This is worth doing for those tricky lighting conditions where you're using spot-metering. You don't want to hold the focus while recomposing only to have your metering blown. On the Nikon camera shown you can have the best of both worlds with the AF-ON button set up for back-button focus and the AE-L/AF-L button locking exposure and focus. But not all bodies have both buttons. My D750 only has the AE-L/AF-L button (which can be configured for back-button focus if that's your preference).
Photo comment By Edward Selfe: Hi Dave - many thanks for taking the time to write a comment and giving your experience of the Nikon system. I am a Canon user, so not as familiar with the capabilities of Nikon, but from my research for this article, I found that all Nikons currently for sale had a button on the back which could perform the AF-STOP function. So I felt that this tip would be useful to all Nikon users as well. However, I hadn't realised that there was the option to customise further, so many thanks for that advice. I would suggest that all users of any camera system explore the customisable function buttons and discover what capabilities can be added! Thanks again Dave. Regards, Edward

Leave a comment

Your Name
Your Email
(Optional)
Your Comment
No info required here, please press the button below.