You may have heard of, or seen other photographers using “back button focussing” but perhaps aren’t sure what it’s about. Here is a simple explanation – maybe you’d like to try it yourself.
Why use Back Button Focusing (BBF) ?
BBF is most useful on moving subjects, so wildlife and sport photography would be good examples.
Consider what your camera does when you press the shutter button – this is the default setup for most cameras ad has been since autofocus film cameras first appeared.
- It evaluates the focus (according to your focus settings), then holds this focus point
- Then it calculates the exposure and locks that in
- Finally when you depress the shutter all the way down, the lens is stopped down to the working aperture, the mirror is flipped (if there is one) and the shutter is fired.
This sequence works most of the time but is has a few minus points
- It can cause a lag between pressing the shutter button and the actual moment of taking the picture. This is because it takes time for the camera's autofocus to work things out. This makes you miss the “critical moment”
- If the subject is fast moving, the delay can cause the focus point to shift by the time the picture is actually shot
- If using continuous repeating shutter modes, many cameras do not adjust focus between shots
- This method gives your brain too much to think about in the heat of the moment – have I got the focus, exposure, framing and timing right ?
What BBF achieves is separation of the focus function from the actual shooting. This speeds things up, gives you less to think about, lets you concentrate on the subject and increases the chances of success.
Setting up BBF on your camera
The camera settings required vary from camera to camera, and depend on there being a suitable button on the camera that can be programmed as the “activate focus” button. There are generally two settings required, plus an optional one.
- Set the focus mode to continuous (My Nikon calls this AF-C)
- Set the button function to “Autofocus on” (My Nikon uses the AEL/AF-L button and calls the function AF-ON)
- Optionally, set up the focussing area to be central to the frame, and leave it at that. BBF avoids the need for complex focussing adjustments.
Obviously the settings will be variable for different cameras, so the best bet is to google search “back button focussing” and you camera model name for instructions. You may well find a YouTube video – there seems to be one for practically every camera model.
Also, if your camera has user-settings modes (mine has U1 and U2) it’s probably worth assigning the settings to one of those so you can quickly switch BBF on and off instead of having to hunt in the menus. For moving subjects I would also set shutter priority for that mode.
Again, the actual settings will vary by camera and not all have user modes.
Using BBF in practice
Once set up, the process is simple but takes some practice to get used to.
- First, frame your subject in the centre of the viewfinder and hit the back button and hold it
- The camera will now continuously track the subject as it moves and you follow it
- When the framing and subject are right, and without releasing the back button, hit the shutter button at the critical moment.
- Some cameras will cancel the focus at that point, some will allow you to continue tracking the subject and shooting
- Release the back button when you are done with that subject/shot
The only disadvantages are
- It takes some practice to get the hang of it
- It will use up the batter faster
- You may need to remember to turn it off again if switching to landscapes etc.
Here are as few useful links - Google search for your own as well
Please leave comments with any other useful links that you may find !