Back-button AF: how to master this professional time-saver
Avoid switching between AF modes and ensure sharp images with this clever back button focus technique. In this tutorial we’ll explain why professional photographers often rely on back button AF to guarantee best results.
If you watch sports photographers, they’ve often got a thumb hovering over the back of the camera, as well as a finger over the shutter release button.
This is back-button focusing, a technique that keeps autofocus locked on a moving subject; locks focus on a stationary subject and recomposes; or keeps focus on a subject if something else enters the frame.
With back-button focusing, you simply press the rear button to lock focus on your subject, take your thumb off and you’ll always keep your original focus point.
If your subject is moving around a lot, you need to keep the back button pressed down all the time to keep focus-tracking (in continuous or AF Servo focus mode), then press the shutter button when you’re ready.
How to set up back button AF on your DSLR
01 Find your AF screen
Every camera model handles back-button focusing slightly differently, but on a higher-end SLR such as the Nikon D600 or Canon 7D, you usually need to assign either the AF ON button (or the AE Lock button) as your main focusing button. We are using a Nikon D800, and we’re going to start by going to Custom Settings Menu>Autofocus.
02 Assign a new button
On the screen that follows, you need to select AF-ON only from the AF activation screen. Doing this decouples autofocus from your camera’s main shutter release button, but you can obviously still use this button when you want to take the actual shot. If you try and half-press it to focus, nothing at all should happen.
03 Set continuous AF
Before you start shooting, set AF mode to Continuous (Nikon) or AF Servo (Canon). This allows you to keep focusing on moving subjects by keeping the AF ON button pressed. To lock-focus a stationary subject, press the AF On button to achieve focus, then release it, allowing you to recompose for a better composition.
04 Important caveats
Now that you’re set up, go and practise! You’ll need to change back to conventional AF activation via the shutter release button if you use a shutter release cable. Also on our Nikon D800, we need to ensure AF-C priority selection is set to Release, again done via Custom Settings Menu>Autofocus.
How to choose the best AF mode
How to focus on off-centre subjects
Creative focus: camera tips for static to spontaneous subjects
Focus modes: how, when and why you need to change your AF settings
How to focus your camera for any subject or scene: free photography cheat sheet
on Friday, October 4th, 2013 at 12:18 pm under Photography Tips.
Tags: camera tips, How to focus