Camera Compatibility

At the time of writing this, the following tutorial applies to the Canon 7D Mark II, the Canon 5D Mark IV and the 1D X Mark II. It’s quite likely that it works on the 1D X as well, and will almost certainly work with future versions of these cameras. 7D Mark III, 5D Mark V and 1D X Mark III etc.

If you have managed to get this working on other cameras, please leave a comment at the bottom so that I can update this tutorial. Thanks 🙂

Confirmed: Canon 80D cannot do double back button AF. It can only do regular single back button AF. Thanks to commenter “S” for testing this and reporting back to me.

Basic Back Button AF

Back button AF is a way of setting up a camera so that the autofocus system is only activated when a button is pressed and held down on the back of the camera. The default behaviour for cameras is for the AF system to begin focussing when you half press the shutter button, but with back button AF this is disabled, and the shutter button only takes the photo and starts the metering.

This decouples the shutter button and autofocus system and allows you to take photos without the camera changing the focus.

Some cameras such as the 7D, 5D and 1D series have a dedicated button on the back of the camera that is labelled AF-On, for use with a back button AF setup. If you aren’t familiar with the technique at all, the fact that many cameras come with a button that is dedicated to this function should tell you how important this technique is for many photographers.

What is Double Back Button AF?

But what about DOUBLE back button AF?  What the heck is that??

With regular back button AF set up, when you press the AF-on button on the camera it will engage whatever AF settings you have currently been using. If your camera is set to AI Servo, it will start the Servo AF system, and it will use the previously selected set of autofocus points.

With Double Back Button AF, you can set a second button (the AE Lock button) on the back of the camera to engage a totally different and pre-defined set of autofocus settings. Including autofocus type, and autofocus point selection.

The best way to have this set up is to enable regular Back Button AF (instructions to follow) and set your camera’s AF mode to AI Servo. Then set the second button so that it calls up One-Shot AF mode, with a single spot-AF focus point in the centre of the AF point array.

With the buttons set up in this way, pressing one button will give you full AI Servo autofocus, and whatever AF points you have been using, and then a quick press and hold of the second button will immediately give you a single AF point in One-Shot AF mode. Never again will you have to take your eye away from the viewfinder to use the menu or dials to swap between these two modes. Now you can do it just by moving your thumb from one button to the other on the back of the camera.

Of course to do this you need to change the function of the AE Lock button, but I find that most people never use this button anyway. If you do occasionally use it, Canon allow you to re-assign its function to another button such as the DoF Preview or mFN button. Problem solved.

How to Set Up Double Back Button AF

Note: The screenshots used below come from a 1D X Mark II. There might be very slight variations on the menu layout for other cameras because the 1-Series cameras have a few additional customizable buttons.

Part 1 – First Button

The first step is to set up regular the back button AF. If you already use back button AF on your Canon camera then you can skip this and move to part 2.

Step 1.

Open the main menu system, navigate to the Orange set of tabs and find the one called “Operation”. Towards the bottom you will find menu item called Custom Controls which is where we are going to make all the magic happen.

 

Step 2.

The very first item in the button list is the shutter button, and the default setting is for it to begin both AF and metering with a half press. By pressing the Set button on the back of your camera, you can change this default setting so that the half-press of the shutter only engages the metering, and NOT the AF.

Step 3.

Move down the custom control menu until you get to the AF-On button. Follow a similar procedure here and set the function of the AF-On button to Metering and AF Start.

Step 4.

You now have regular Back Button AF set up, so you should test this to make sure you selected the right things. Make sure your lens’ autofocus is on and half press the shutter button on the camera. If you have done things right, the camera will not change the focus of the lens. Now press the AF-On button on the back of the camera, and you should see the focus change.

If this isn’t happening, repeat the previous steps and make sure you follow the on-screen instruction for saving the settings. If you don’t press “Set”, and simply press the menu button to go back in the menu system, the settings will not have been saved. This is the most common issue people have when trying to get this set up.

Part 2. – Second button

 

Step 1

Back in the custom control menu you need to select the AE Lock button which is the one with the star (*) on it. Again, change this to “Metering and AF Start”, but this time you’ll also notice at the bottom of the screen it says to press the Info button to set details.

Step 2

Press that info button while you have the AF and metering start option selected. This will open a new screen where you can define the exact autofocus mode that you want to be engaged while pressing the AE Lock (*) button. My recommended settings can be seen the screenshot. You can see that I set it to One-Shot, and for AF Selection Mode I have it set to a single spot-AF point which is the most accurate AF point that these cameras have.

That’s it! Now a press and hold of the AE Lock button will call up those autofocus settings. Of course you might have some very specific needs that require you to choose some different settings, but personally these are the ones that I find work for a really broad range of photography. You have AI Servo ready to go for fast moving objects using the AF-On button, and you have One-Shot AF ready to go on the AE Lock button with the super accurate spot-AF point when you’re working with static objects, or perhaps portraits with a shallow depth of field.

I’ve always been a back button AF user, but the introduction of this additional option really  puts me in a better position when things are happening quickly in front of my camera and I need to make rapid changes to my autofocus system.

Part 3 – But Wait! There’s More…

I guess I could almost have called this Triple Back Front AF, but the name isn’t very catchy and it’s kind of confusing. The cameras that allow AF function assignment to the AE Lock button also allow you to assign some alternative functionality to the DoF Preview button. I never really use that button with the default DoF Preview feature, so I also use this customization option to create what I call my “Oh Sh*%” AF button.

Step 1

Select the DoF Preview button in the custom control menu and choose the option that has the letters AF and two arrows. It’s called “Switch to registered AF Function”.

Step 2

Press the Info button to set the details for the button. It works slightly differently to the one that we assigned to the AE Lock button in that you can’t define an AF mode (AI Servo, One-Shot etc), but you can define a set of AF points to call up, and you can even adjust the tracking and point switching speeds for those points.

The versatility of such an option is quite mind-boggling, but after some careful thought I chose to use it to call up the full set of AF points, instead of a cluster or a single point. Here’s why: Normally when I’m working with AI Servo AF I’m working with a small cluster that I place in the frame very specifically. A small cluster is more accurate and acquires focus lock much quicker. Occasionally though, you might have an extremely erratic subject that suddenly does something unexpected. This is where I use my “Oh Sh*%” button! If that ever happens, by pressing and holding the DoF button, it engages the full array of AF points and overrides AF point selection that I was using before. It’s only active while you hold the button down, so you can use it briefly if something suddenly strays outside of the AF point cluster you have been using.

Here’s a scenario to think about: You’re photographing an eagle sat on a log. It’s pretty static and has been for some time so you’re working with the One-Shot AF button that you set up in Step 2. All of a sudden the eagle flaps its wings, dives off the log and flies right at you! The size of the bird in the frame is changing rapidly and you haven’t had time to pick an AF point cluster and plan for this! Instead, you press and hold the DoF button to engage the full AF point array, and you move your thumb to the AF-on button to start AI Servo autofocus.

It might not be the ideal AF scenario because using a small cluster is usually better when you can, but for unexpected moments, it might just get you the shot you would have otherwise missed.

The customization options of Canon’s higher end cameras are pretty incredible, but some of the options are buried pretty deep in the menu system and you have to really think hard imaging how you might use them. Out of all my customizations though, double back button AF is by far my favourite! Give it a try and let me know what you think.

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