Back button AF – do you love it or loathe it?
Back button AF is a polarising capability – some photographers, me included; love it. Others just can’t see the value or get over the initial awkwardness.
What is back button AF?
In short back button AF moves the control of when a camera is actually autofocussing to a button on the back of the camera. Most often the AF-ON or exposure lock [*] buttons. In parallel the shutter or “front button” is often reassigned to not actuate AF at all.
As a result you can always use AI Servo tracking focus AF and if you shoot static subjects just release the back button when the subject is in focus. Then you can recompose the frame as you like.
If your camera is used only by you, or another photographer familiar with back button AF then do the change and persevere until you get it.
If you are one of the photographers that sometimes need to pass their camera to a friend or family member who has a different level of photographic knowledge this is where you run in to problems. A camera configured with back button AF almost always results in out of focus pictures when used by inexperienced users.
EOS 7D Mark II = back button AF Mark II
The EOS 7D Mark II has implemented what can only be called Back button AF Mark II!
With the EOS 7D Mark II the level of adaptation possible with the camera controls settings is the most I have ever known:
EOS 7D Mark II is more flexible than an EOS-1D X
Firstly, you can configure the characteristics of the AF-ON and exposure lock buttons [*] totally differently, not just one is AF and the other is AE-LOCK. Each button can have different back button AF characteristics. This is what makes it so powerful.
For the AF-ON and the AE-LOCK [*] buttons you can individually set the AF start position, the AI Servo AF characteristics, AF Operation and AF area selection mode.
AF start position
When you press the back button the camera can be set to keep using the currently selected AF point, or can jump to the registered AF point.
I leave it to stay on the selected AF point, but it does remind me I need to write about registered AF points soon too.
AI Servo AF characteristics
The AI Servo characteristics option opens the opportunity to switch to a different AF Case quickly or stay with the one you have already chosen.
AF cases are important to understand and adapt to the subjects you photograph. Each AF case has three tuning parameters associated with it.
AF operation
This is the key for me – pressing the AF-ON or [*] button can be the trigger to switch to AI Servo AF. If you use back button focus with Servo AF then set the buttons to do that all the time. You will then avoid the nightmare of thinking you are doing back button AF with AI Servo only to find that you set the camera to ONE SHOT and your back button AF is now working with one-shot and not tracking.
I’ll own up and say “been there done that…” but I never will again with making sure my back buttons also force the camera to AI Servo mode.
AF areas selection mode
Yes you can also have the press of the back button switch to a preselected AF pattern. Depending on your manual and mental dexterity you could set the AF-ON button to have one AF pattern and the [*] button to select another as a way to quickly change from one setting to another.
It’s certainly less clicking than even moving the AF area direct selection lever on the back of the camera. I still haven’t trained my thumb to find that control reliably, plus it means taking my thumb off the AF-ON button.
Still reading?
Wow you made it this far; thanks. This is the section you will love if you ever need to ask someone else to take a photo with your camera.
You can set the camera to ONE-SHOT AF mode as the default, and you can make the shutter button activate AF. The camera will autofocus and lock the focus just by pressing the shutter.
However when you the super trained experienced photographer pick the camera up and use the back buttons to control the AF it switches to AI Servo AF and back button focus.
This is ideal if tracking a subject is what you need – but I found a small “wrinkle”. If you use back button focus to focus on a subject, lift your thumb off the back button and recompose, when you press the shutter the camera will focus on the subject in one-shot again… Maybe it’s better to leave the camera in AI Servo too.
Getting in some practice
I’ve been out with the EOS 7D Mark II just once with the intention of working through my understanding of the AF and the practicalities. I’m finding that the auto point selection in area or wide area AF area modes is pretty good at “reading my mind”. I was walking back to the car and saw something in a field across from me, raised the camera to my eye hit the back button and pressed the shutter. The bird is a big one, but a long way off and small in the frame. The AF identified the subject and focussed on it, even when easier more contrasty subjects existed in the frame.
Screenshot of DPP showing the AF point automatically selected by the EOS 7D Mark II
If you don’t have an EOS 7D Mark II then get one 🙂
I don’t have an EOS 7D Mark II how do I set up back button AF?
You need to read these articles for the EOS 7D, EOS 5D Mark III and EOS 650D/700D or this one for older cameras like the EOS 5D Mark II and EOS-1D Mark III and EOS-1D Mark IV.
Great article Brian. Well explained and easy to understand. I am still learning the camera. I now find C1-C3 functions invaluable for testing and seeing which way I go with my understanding of the camera. Thanks for taking the time to write this up.
Great article
I have a7D Mark ii and one button on the back is already set for one shot focus I would like to use the other button for A1 servo.
Maybe I am confusing the issue, am I right on thinking that what tour saying is that you can assign the one button to do both one shot and a1 servo modes.
I have only just read the article so have not had the chance to play around with the camera as yet!
Hope I made what I want easy to understand!
Once I get home I will have a play around to see if I understood the article it was definitely easier than the Canon manual!
Hi Nigel,
In reality using back button focus my camera is always in AI Servo focus mode. When I want to track a subject I keep the AF-ON button pressed down, when I want to focus on a subject I press the button down, wait until the subject is focussed then release the back button. Now I can reframe and the camera won’t keep focussing.
Hope that clarifies it for you, and thanks for asking.
Brian / p4pictures
G’day Brian and thanks for your comprehensive explanation of back button. I am stuck, and so are a couple of my mates with their new 7D MkII as we can not find that first black, with orange, detail set on our menu systems anywhere. It is the first one headed Detail set and has the four menu items starting AF start position and ending AF area selection mode. We all have firmware version 1.0.4
Yours in hope, some confused Ozies.
Regards
G’day Stuart, thanks for asking the question. I’m sure it’s not just you and your mates having trouble so here’s the help.
Access the custom controls screen, either from the camera custom functions or from the quick control display on the rear of the camera.
Then when you choose to configure the AF-ON or * button to be Metering and AF start at the bottom of the screen there’s a note that says INFO Detail set. and that is where the screen you see at the top of the post appears.
I’ll also add a screenshot to the post later.
Brian / p4pictures
If you want to be able to use the back button af and recompose, you have to set the shutter button to metering start instead of metering and af start. That way the shutter button is only used to to release the shutter
Thanks Brian
You always make perfect sense!
I’ve just bought the 7D mark 11 and I’m getting to grips with the camera and settings.
I’m looking forward to trying out back button focus!
Hi Brian,
If I want to stay with the composed background but allow the subject to run across the composed background.
Should I set up as described,got the focus on the subject,then should I release pressing and let AI servo track on its own across the screen on all available focusing points or keep pressing pressing back button down?
Thanks,
Rita
Hi Rita,
If you take your thumb off the AF button then the camera stops focussing… You need to have the back button pressed or the camera won’t know you want it to focus / follow the subject as they move across the frame.
Brian/p4pictures
Dear Brian,
Thanks for the article. I have a question about the paragraph just above ‘getting in some practice. You write: ‘This is ideal if tracking a subject is what you need – but I found a small “wrinkle”. If you use back button focus to focus on a subject, lift your thumb off the back button and recompose, when you press the shutter the camera will focus on the subject in one-shot again… Maybe it’s better to leave the camera in AI Servo too.’
My question is: back button focus has been set to AI servo, so that is for moving objects. The shutter button has been set for AI One Shot, so that is for still subjects. Recomposing while a subject is moving can be hardly done – while recomposing, the subject will move out of focus and since you don’t press the back button anymore, the camera will not refocus again. In those cases, can’t you just use the shutter button to focus, recompose and shoot the picture?
My second question is: while using your setup (back button focus in AI Servo and having also focus assigned to the shutter button though in AIO One Shot), will the back button focusing be overruled by pressing the shutter button, which you need to press for taking the picture?
Looking forward to your response,
Regards,
JB
Hi Jeroen,
Firstly the button that was pressed first takes priority if both are pressed. So if the back button set to AI Servo is pressed, then using the shutter does not switch the camera to ONE SHOT.
However if you want use focus lock and recompose, then keeping the shutter button active allows this, but remember that its one-shot. So you’ll be pressing the back button for tracking, and if you decide to not track the subject then using the shutter as normal is for static subjects.
Brian/p4pictures