Back-button focus: why many pros separate focusing from the shutter
Back-button focus moves autofocus to a rear button so the shutter only takes the picture. Here is how to set it up and whether it suits you.
By default, half-pressing the shutter focuses the camera. With back-button focus, you assign autofocus to a button on the back, such as AF-ON on Sony cameras, and the shutter button only takes the picture.
Advantages
- Focus once, then shoot as many frames as you like without refocusing.
- Switch between single and continuous behavior without menus: hold the button to track, release it to lock.
- Avoid the camera refocusing on the background when you recompose.
Disadvantages
- It takes a week or two to retrain your thumb.
- Lending your camera to someone else becomes confusing.
How to set it up on Sony
In the menu, set AF w/ shutter to Off and assign AF On to the AF-ON button. Set focus mode to AF-C. Now hold AF-ON to focus and track, and let go to lock.
Who benefits most
Wedding, event, sports and wildlife photographers who constantly switch between moving and static subjects. Landscape and product photographers gain less, since AF-S with the shutter works fine for still subjects.
Next: Dynamic range: photographing bright skies and dark shadows together
