This post is about the AF-ON button or back button focus. If you already use this technique – go and make yourself a martini!
Before computers enabled auto-focus systems in cameras, the photographer had to manually focus their lenses and the process of taking a picture involved four steps: set the exposure, focus, compose and release the shutter. Today, it still requires these four steps but our modern digital SLR cameras have simplified it to two actions: compose and press the shutter button. However, behind the scenes, the four steps are still there, but just done by computers. And therein lies a big problem.
I’ve met many photographers who are not setting up their cameras to shoot sports that would maximise their opportunity get great shots. In fact, they’re using a $6000 camera like a $500 manual film camera. Well, maybe not that bad, but almost. In this post I’m going to write about one of these settings: why you should not use the standard “half press shutter” to auto-focus in sports photography.
Auto-focus out of the box
Out of the box, every digital-SLR is set up so that the shutter button does three things. Yes, three – count them: 1. When you press it half way down it activates the auto-focus function; 2. It starts the exposure meter and the exposure programming if you’re using an auto-exposure mode; and 3. When you press it all the way down, it fires the shutter and writes the images out to the memory card. You might ask what’s wrong with this? Well, remember that taking a photo before computers was four separate steps? The main problem with putting three steps into one is the loss of control in the two steps of focus and compose:
- Focus. In sports, your camera is almost aways set up to use continuous auto-focus (AF-C on Nikon and AI Servo AF on Canon). This allows the camera to track, or keep focus, on moving objects like an athlete or racing car. Of course, continuous auto-focus (I’ll use AF-C as a shorthand) has been one of the biggest breakthroughs in digital SLR technology and that’s why the best camera bodies cost $6000 or more, and sports photographers use this feature, but when you link AF-C with the half-press shutter it doesn’t work for a lot of shots. I’ll explain why and how to fix this below.
- Compose. Coupled with focusing, with the current AF-C systems it is either impossible or not practical to compose a photo where the subject is in focus and not positioned at the selected focus point when the half-press shutter button is used to activate auto-focusing. Again, more below.
Since 1989, all Canon EOS cameras have been able to be set up by the user so that a button on the back of the camera near where the right thumb usually rests is used to start the auto-focus function. Nikon also have this in their d-SLRs. According to Canon, this feature appeared through feedback from their professional sports photographers. This button is sometimes called “Back button AF” but on both camera systems the button is labeled “AF-ON”. This allows the photographer to start auto-focus by pressing the button, but equally important, to turn OFF the default setting of having the half-press of the shutter button starting the auto-focus. By turning off auto-focus on the shutter button means that the photographer can control when to stop and start focusing. Auto-focus starts with you press the AF-ON button, if you keep it pressed, and you’re in AF-C mode, the camera will keep focus on the object, and here’s the most important bit – the camera will stop auto-focusing when you release the AF-ON button and the focus will not change.
Practically, the situation where it’s most important for sports is when you’re tracking a moving object like a runner and out of the corner of your eye you see another object that’s going to cross in front of your object and your camera. This means that your camera is going to change the focusing from your runner to the interfering object. In this case, you just take your finger off the AF-ON button and keep shooting with your shutter button. If you hadn’t disabled auto-focus on the shutter button, all your shots will be out of focus because you wouldn’t have been able to tell the camera to stop auto-focusing and the interfering object will be focused instead of your object.
Here’s the magic setting to disable half-pressed shutter focus:
Function a5: AF Activation. Default is Shutter/AF-ON, change to AF-ON only
Custom function – C.Fn IV-1 Shutter button/AF-ON button. Default is 0, Metering and AF start. Use 2, Metering start for the shutter button and AF for the button. More info here.
Most sports photographers use the center focus point and when shooting fast moving sports you don’t have time to move the focus point around. What do you do when you want to compose your shot so that the object you want to be in focus isn’t in the middle of the photo (of behind the selected focus point)? Well, if you’re using half-press shutter button for auto-focus and you’re in AF-C mode you’re out of luck. You can’t, as when you recompose, the camera will just keep auto-focusing and focus on whatever is now in the middle of the photo or behind the focus point. But, if your using the AF-ON button and disabled auto-focus on the shutter button it’s super easy. Just tap the AF-ON button to focus – don’t hold the AF-ON button down. After focus has been achieved just recompose and press the shutter button. Pressing the shutter no longer tells the camera to activate auto-focus. In fact, this method makes the AF-S mode on a Nikon and One-Shot AF mode on a Canon redundant. The AF-ON button has duplicated this single shot auto focus mode. This technique is also useful for portraits and situations where you want to re-compose your shot after focusing and you don’t have time to set up the shot and manually move the focus points around.
Let me know how you go.
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19 thoughts on “Syd: Use a different button to focus”
Excellent article!I started using the AF-ON button to focus a while ago and the results were by far better than just using the shutter button to focus.Thanks for this great info!!
Glad you enjoyed it.
Hey Syd and Ryu I know you want us to give you ideas for future articles and podcasts topics.I was wondering if you could make an article or better yet talk about it at the next podcast,about composition in sports while using super telephotos.How do you compose when working with a 300mm+ lens?I just recently bought a Canon 400mmf 5.6 L which of course I will only use outdoors during daylight because of the aperture,but have not had the chance yet to start photographing the sports I want.I took a few pictures of a paintball tournament and even though I got some keepers,I had quite a few pictures where I couldnt get the whole subject in the frame due to the long focal length.Any tips from you guys will be highly appreciated.
Will do Assiel!
Enjoy your new lens in the mean time.
Thx for the great article !
I never heard about this tips (i’m novice).
I will try it next game I shoot.
You’re welcome – let us know how you go. Post your pics in Flickr and we’ll keep an eye on it.
Thanks so much for posting about this. I switched a few months back to BBF and I love it. I find that I get many more quality shots from it.
Although, I still feel like I’m missing something. I still quite a few that end up out of focus. I shoot Canon, I use to use AI-Servo mode, but lately I’ve gone back to one shot because I like the comfort of seeing which focus point its choosing. Does it really matter what mode I shoot in?
Also, I find myself most often, pressing the Af-on button, then releasing while I track my subject and hit the shutter. Should I be holding it down? I’m confused a little. Could this be my focus problem?
Again, I’m just a momtographer, trying to get the best shot of my soccer star. Thanks for your help!
You should be holding the AF-ON button down if you want to track a subject in AI-servo mode. As soon as you let go of the button the AF will stop.
Shooting action with One-shot is like driving an automatic shift in manual. Keep persevering with AI-Servo.
You should be setting up your camera to use the center focus point in AI-Servo – it will always use that point so there’s no benefit in One-shot.
Did you read the posts on
I discovered this feature about a month ago and when my thumb is in the right place, it’s great. I’m still working on finding AF-ON by feel. I’ve missed a couple of shots because I accidentally hit the AE-Lock instead. Prior to using AF-ON, I would focus on an object (e.g. 2nd base if I think something interesting is going to happen there) and then flip the auto-focus switch to manual.
I just noticed my Canon battery grip for the 40D does not have a AF-ON button for when shooting vertical.I guess Ill just have to shoot mostly on horizontal.
@Michael – using the back button focus technique means you won’t need to flip the AF to manual
@Assiel – unfortunately only the pro-bodies have a vertical AF-ON button.
Except for the 7D vertical grips.Just saw a few of those from different brands and saw the button there.That made me check if mine had one but unfortunately just the pro bodies and the 7D have it.Oh well one should make the best out of the equipment each one has.
thanks syd for your help. I think my most recent frustations with BBF and Ai-servo came from user error. After feeling totally down about my skills, I remember that I had set my focus points to manual focus when I was attempting macro photos. This should be a lesson that I should stick with action shots!
Lisa – we’ve all had these moments! I remember getting a loaner body and couldn’t figure out how to set the shutter speed and had to ask 3 other shooters. Turned out when it said 30, it was 30 sec not 1/30th of a sec! Doh
You just need to shoot so often and know your equipment inside out and have muscle memory so you can check all the settings every time you pick it up. With practise it’ll become second nature.
Hi, I get everything you say until this point , “After focus has been achieved just recompose and press the shutter button” Surely by the time you’ve recomposed you moving subject is either nearer or further away, and if shooting wide open, will be OOF, or am I missing something?
Mark – that para is about using the back focus button in a way to remove the need to use Single Shot – eg when shooting a portrait or a static subject. If you’re shooting a moving object then you have to keep the back button pressed, but a static subject you can release the button and then the camera won’t try to focus again when you press the shutter.
I had heard about this technique before but your post decided me to try it. It is nice and yet not an all-times lifesaver. For example, if I want my subject to be on the right of the frame, I still have to move the focus point to the right, where I want it, before I activate auto-focus. The “tap” trick will not work with moving subjects because between the instant you “tap” the AF-ON button and the instant you activate the shutter, the subject will have moved. Therefore, you will indeed need to use AF-C, and that means positioning the focus point to wherever in the frame you want the main subject to be.
Hi Dominique, you’re absolutely right. The ‘Tap’ only works for stationery subjects.
But for stationery subjects you don’t need to move the focus point. Leave it in the middle. Tap to focus and then recompose.
For moving subjects you will need to keep the button pressed.