What is Back-Button Focusing (BBF)?
With most cameras, you depress the shutter button half way to focus and then to actually take the picture the button is pressed the entire way. With back button focusing, you use (as the name implies) a button at the back of your camera to control the focus, taking it away from the shutter button entirely. I recommend using BBF in continuous auto focus mode (that is AF-C on Nikon, AI-Servo on Canon).
Why Use BBF?
Lock Your Focus For Re-composition
It’s much easier to lock your focus with back-button focusing. We often want things off centre and have to hold the shutter button half way until we reposition. With BBF, once you’ve locked your focus you’re free to move left or right and shoot off centre as many times as you like without having to re-focus.
The same applies when you’re waiting for something to happen or move; you don’t have to wait with the button half pressed. And if something moves in front of your shot, you don’t have to worry about re-focusing once it’s moved. It also helps to stop the focus confusing itself and hunting in a ‘busy’ setting.
If you’re worried
about tracking action shots then you can still do that in the same way; just
holding the back button down rather than the shutter (if you’re shooting in
AF-C/Al Servo as recommended earlier).
Switch From AF to MF More Effectively
Switching from auto-focus to manual focus becomes much easier. Usually you have to flick a switch to MF otherwise the autofocus would just override it when you pressed the shutter. If you’re using the BBF and want to switch to manual, you can just turn the manual ring on your lens and use the shutter without AF interfering.
One thing I’ve found particularly handy with this feature is when it’s used with a filter. I sometimes use a 10 stop ND filter: I ahve to focus on my subject before I put the filter on, otherwise I’d just see this:
Not so helpful. Using
back button focus means once I’ve got the focus correct, I don’t have to worry
that pressing the shutter button will make it readjust once I have the filter
on and try to take my shot.
It sounds silly, but ergonomically it’s pretty good too. It may not feel right at first, but in time it actually became more comfortable for me than shutter focus. Plus, it ever so slightly shifts the weight balance so it can even reduce hand shake in images!
How to set up BBF
Okay, I’ve convinced you of the joys of BBF hopefully, so how do you set it up on your camera? Most high end DSLRs will have a button already dedicated to this labelled AF-On or similar.
Don’t worry if yours doesn’t, you can often still nominate another button to do it, just check your manual.
You’ll still need
to make some changes in your menu. Canon users, you’ll find it in your Custom
Controls section; change your shutter button function to Metering Start Only
(without the AF). I have a Nikon D800 so here’s how I did it for mine: Autofocus > AF activation > AF-ON only > OK
It doesn’t come easily, exactly, switching between shutter focus and back button, butit's worth it. When I made the change I still found myself furiously pressing the shutter for a second before the realisation dawned on me. I also took a few out of focus pictures initially due to forgetfulness, so I don’t recommend you try this out at an important gig. It’s worth giving it a go though, it just takes patience and practice. The benefits are numerous, from easier re-composition to being confident your shot is still in focus after putting a filter on. For me, it's actually a more comfortable and natural way to hold my camera too, particularly when I have a heavy lens attached, so I hope you find this is the case for you too.