Using back-button focus (BBF) on your Canon camera
There are two ways to initiate (and lock) focus on your Canon DSLR
- using the shutter button, and / or
- using the AF-ON button on the back of the camera, near your thumb.
The AF-ON button can be set to be the only way to initiate focus, disallowing the shutter button from doing so. Depending on how you program your camera, the AF-ON button could allow you to trip your camera’s shutter independently of your focusing. Whether this is useful to you, (or perhaps even cause problems for you), depends on:
- your style of shooting, and
- the focusing mode that you use on your camera.
Let’s break it down …
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At some point, photographers who become frustrated with soft images, will look at solutions online on how to get crisply focused images. One of the pieces of advice that is often given, is to use “back-button focus”, rather than using the shutter button to initiate and lock focus. This may, or may not solve the problems they have.
As mentioned, you can initiate and lock focus with the:
- shutter button, and / or
- AF-ON button
How they affect you, will also depend on whether you tend to shoot in:
- Single mode, or
- Servo mode
Servo + AF-ON
Sport and action photographers will predominantly shoot in Servo mode. It makes sense because they most often shoot moving subjects. Then while they keep the AF-ON button pressed in, and while in Servo mode, the camera will attempt to track focus. In other words, the camera will continually refocus the lens to keep the subject in focus.
Now, the beauty of working this way, is that you can lock focus simply by not pressing the AF-ON button. If you’re doing a static portrait, you’d focus on your subject’s eyes, and then let go of the AF-ON button. Your focus is now locked.
This works beautifully for Sport photographers – they keep their camera in Servo mode, and then use the AF-ON button to track focus. The moment they photograph a static subject (or want to lock focus), they let go of the AF-ON button.
Servo mode is “Release Priority”. The camera’s shutter will fire, regardless of whether your subject is in focus or not.
There’s a downside to shooting in Servo mode and using the AF-ON button … your flash won’t emit the red AF-assist beam to help your camera focus. This is a real problem in low light events where you use flash. Your camera “thinks” it is in focus, and because it is release priority, the shutter will fire. And this is done in low light without the benefit of the AF-assist beam. This is a recipe for a lot of mis-focused images.
With Servo + AF-ON, the camera might have a tendency to keep hunting for focus in low contrast scenarios, often enough resulting in slightly mis-focused images when you trip the shutter while the camera isn’t accurately focused.
Single + AF-ON
This works in a similar way to Servo + AF-ON, with this exception: In Servo mode, the camera will continue to refocus while the AF-ON button is pressed. With Single + AF-ON, the camera will focus, and then once it is in focus, stop refocusing.
Now, if you let go of the AF-ON button, it will essentially lock focus. (The shutter button now doesn’t refocus the camera.)
In Single + AF-ON mode, the camera will make sure to lock focus before confirming that it is focused via the green dot in the viewfinder. (With Servo + AF-ON, the camera could keep refocusing, potentially giving you slightly mis-focused images.
With Single + AF-ON, the speedlite will emit the red AF-assist beam, giving you a better rate of success when focusing in low light.
Back-Button Focus and me
After decades of shooting with the shutter button as the way to acquire focus, I haven’t been able adapt to using the AF-ON button. I therefore use the shutter button to acquire and lock focus.
Ultimately, if you’re exploring the BBF option, you have to see which method works for you. If you’re a sport or action photographer, then using the BBF method with Servo mode, makes a lot of sense.
About the choice of using Servo or Single mode - since I mostly shoot events and use flash, Single focus mode is what works best for me. I need that AF-assist light from the speedlite. I need that.
How to set BBF on the Canon 5D mark II.
(It is very similar on all the Canon D-SLRs)
Custom Function IV – 1
Options 0 and 1, will allow the shutter button to initiate AF.
Options 2n and 3, will not allow the shutter button to initiate AF – so this now means only the AF-ON button can start the AF.
Custom Function IV – 2
This allows the * button (AE lock), to swap function with the AF-ON button. Whichever is more ergonomic for you.
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There is another way of doing this: the same button can be programmed not to initiate but to STOP the autofocus action (I am not sure that you can do this with the 5D, but on the 1D it is the way I use it when I shoot action).
This way, I normally use the shutter button to initiate autofocus, and usually release the shot without using the back button. In a rapidly changing situation, I have a very quick and easy way to lock focus in an instant, using the back button, without taking my eye from the viewfinder. I used to do this by keeping the thumb of my left hand on the lens AF-M switch, so that I could turn AF off using the mechanical switch, but this is not a good way to do this. It is much much better to use the back button-you only need one hand, you can’t miss it, and you can release it again to initiate AF again.
Try it-you might like it.
Comment by Costas — August 29, 2012 @ 5:13 am
Never knew, I am going to give it a try next time I am in need of Servo. Thanks Neil, love the blog!
Comment by Eric — August 29, 2012 @ 8:10 am
I started using BBF last year when I did some concert photography. Worked like a champ. Haven’t gone back. It’s my new habit.
The downside is that I tend to hold my camera tighter when I use it now. The rubbery grip next to the button became unglued and fell off from, I presume, the extra pressure and friction. There’s some looseness to the rubbery grip on the front of my battery grip, too. ::sigh::
Comment by Augie De Blieck Jr. — August 29, 2012 @ 9:49 am
I’m a nikon shooter. Will VR work on VR lenses using BBF on the nikon D700 or D800?
Comment by Wayne Bennett — August 29, 2012 @ 1:51 pm
With 5D Mark III, the depth-of-field test button can be reprogrammed as a Single to Servo switch when pressed. Since it is now easily accessible without leaving the viewfinder, shifting from static – movement AF configuration is really a piece of cake. In addition to AF accuracy improvement, this has been a big change compared to my previous 7D.
Comment by Julien — August 29, 2012 @ 2:45 pm
I love the BBF. I started using it for sports and AI Servo, but I liked it so much that now I use it all the time. It turn somethings much easier, like “focus and recompose”, and for adjust the focus manually (when using FTM focus lenses). But it takes some time to get used to it.
Comment by Humberto Teté — August 29, 2012 @ 8:06 pm
I have to agree with Costas at #1.
Since Servo mode is though for moving targets that only occasionally will stop, it make sense to have the most comfortable position of your hand (only index finger working) leaving the focus hunting. When your target actually stops, then pressing the AF-ON button will stop AF. Note that having both the shutter release and the AF-ON button depressed is actually quite comfortable, resembling the pinch action, thumb against index finger. I can hold this position for minutes at a time for the whole day.
Julien at #5: I actually use the DOF test button (and yes i use the 7D, but i can still reach it with my left thumb while holding my heavy lens with my left palm up and index pointing forward, in a stance that resembles the stance of a biathlon shooter) to temporary change from single focus point to area. Very useful when shooting birds: single point for birds on the ground (either static or walking around); area focus for birds in flight (when you don’t have to worry about focusing on something else)
Comment by Marco — August 29, 2012 @ 10:45 pm
For many years, I use the back-focus button now. I use a single focus point to know exactly where the focus is.
Workflow with auto-exposure (Av, Tv or P):
- focus (single focus point)
- exposure (half-pressed shutter)
- aim (compose)
- wait (for the right moment)
- shoot
Workflow with manual exposure (M):
- exposure (manual)
- focus (single point)
- aim (compose)
- wait (moment)
- shoot
If the subject moves a little, I just mimic by moving a little too. That way, I keep focus, I keep composition and I keep exposure (manual, or half-pressing the shutter).
And for snapshots it’s: exposure-focus-wait-aim-shoot-wait-aim-shoot-…
Comment by Frank — August 30, 2012 @ 2:01 am
I switched to BBF a few years ago with my old 550D and have used it on ever body I have had since, up to and including my 5Dmk3.
Personally, I find it much easier to get keepers using BBF than I ever did with the half pressed shutter method. But from what I gather, it isn’t for everybody.
Great article and very informative.
Comment by Johnny WashNGo — August 30, 2012 @ 11:05 am
I started photographing 4-5 years ago, and from day 2 (when I discovered its existence on my new Panasonic FZ-18) I shoot only using BBF. This of course carried on on my 40Ds.
It makes perfect sense having two different controls for focusing and tripping the shutter. To me, they are two different processes, that can happen in completely different times – so, it only feels natural to keep them apart.
When things run slowly, I want to focus on my subject (with the BBF) and then wait for the perfect moment to press the shutter (by the way, keeping it half-pressed locks my exposure, if I need to).
When things run fast, I either press the BBF repeatedly or keep it pressed (AI Servo a.k.a. mixed mode, usually works well enough) and know that most probably I will be focused when the time comes to take the photo.
Comment by Iosif — August 30, 2012 @ 6:15 pm
Thank you so much for this info, use backbutton focus already for quite a long time, but almost never shoot flash. Two weeks ago i’ve had some trouble focusing and now i understand that it was because i’ve put my camera in al servo mode! Problem solved! :)
Comment by Hanneke — September 6, 2012 @ 9:36 am
The biggest hurdle I’ve faced in using the AF-ON (back-button) focus is that if I ever hand my camera to anyone else to take a shot with me in it, we’re either going to have a bit of an information session so they understand what they’re supposed to do or we end up with a blurry image. Or, as usually happens when someone who’s used to holding an iPhone is given a D3s and 70-200 to try to keep still, both…
Comment by Darryl — September 7, 2012 @ 2:54 pm
There is a third AF mode on my 40D, “AI Focus”, which combines single and servo. You can still select your focus point and you still get the AF-assist beam but if the subject starts to move after the initial focus lock the camera transitions to servo mode. I would assume the other Canon cameras have this option and I have found it gives me the flexibility (with BBF) to shoot everything from landscapes to the bride and groom dancing at a wedding.
Comment by Matt Regan — September 11, 2012 @ 1:29 pm
Neil, this one post was worth the price of admission. The number of tack sharp images I’m delivering as a second shooter is up substantially using the advice on this topic. I also took your advice about “Turning off Motor Mode” and my total shoot count is up also.
Thanks.
Comment by Clarence Butts — September 24, 2012 @ 10:52 am
Neil,
i am glad you mentioned the custom function for switching * and AF-ON. Some of the Canon battery grips do not have the AF-ON button (only two of the three buttons). To keep the BBF function with the grip and portrait orientation you need to switch AF to the * button. Not sure why Canon didn’t put the three buttons on the battery grip – they probably saved a buck and a half or the equivalent in Yen. Not doing the switch is sure to generate a loud WTF moment when you first try BBF with a battery grip.
Ed
Comment by Ed Gill — February 19, 2013 @ 6:33 pm