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.
Here I wanted the rocks in focus and using BBF made it much easier to shift my composition once I had them right.
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.
Filters
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:
Focusing your shot with a filter can be tricky..
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.
A long exposure which used BBF to focus before attaching the filter to the camera
Much better.
Ergonomics
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!
Holding the camera using back button focusing eventually feels pretty comfortable
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.
Many cameras will have a dedicated button but if not you can still assign your own
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
Custom Setting Menu > AutofocusAF ActivationAF-ON only
Conclusion
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.
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