If you use a modern DSLR or a Mirrorless Camera, it can come with a focus button identified as “AF-ON”. While this button may seem redundant at first glance, it can be a very useful feature that will make it easier to focus on an object. In this article, I’ll explain what the AF-ON button is and how you can take advantage of it on your camera.
What is the AF-ON button?
On all modern Digital Cameras, the AF ON button stands for “Autofocus On”. It is used to enable autofocus and metering, although its function can be reprogrammed for some other purpose in more advanced Digital Cameras.
Once the shutter release is set to turn on autofocus when pressed halfway down by default, the back button is redundant unless the focus is unbound from the shutter release or performs some other function. When the focus is decoupled from the shutter release, it basically becomes a setting for focusing on the rear button.
Although many photographers, including me, use this button to focus, it can be programmed for different functions such as autofocus or auto exposure lock.
Focus back button settings in the camera menu
In the next sections, we’ll take a closer look at where you can access the rear focus button settings in the camera menu when using models from different manufacturers.
AF-ON Canon button
If you use a Canon DSLR or a Mirrorless Camera, you can change the behavior of the AF-ON button through the “Custom Controls” flyout of the camera menu. After navigating there, you’ll find the AF ON button setting as one of the selections:
If you have a Mirrorless Camera, such as the Canon EOS R6, the custom controls page will look slightly different. However, the af-on button name will still remain the same, as shown in the image below:
To set the camera to rear-button focus using the AF ON button exclusively, you’ll need to perform two steps. First, you’ll need to navigate to the first shutter release option and then set anything other than “start metering and AF start” (I set mine to “AE lock”). This unlinks the focus of the shutter release button and activates the auto exposure lock when pressed halfway through.
Second, you will need to navigate to the AF-ON button option and set it to “start measurement and AF”:
After doing this, the camera will activate autofocus when the AF-ON button is pressed, effectively activating the rear button focus.
AF-ON FujiFilm button
FujiFilm users have two ways to set up the rear button focus. The first method (and what I prefer to use), is to switch from auto focus to manual focus using the button in front of the camera (position “M”). If the camera has an AF-ON button, this button, by default, turns on autofocus even when the camera is set to manual focus. This allows the AF ON button to be used easily for the rear button focus. The only thing you need to be sure of is that the AF-ON button is set to “AF-ON” in the camera menu (found in Setting -> Button Setting/dial -> Function Setting (Fn)), as shown below:
If you prefer to configure this button for some other function, you can navigate through many different selections:
The second method is to unlink the autofocus from the shutter release button. After doing this, pressing the trigger halfway down will not cause the camera to focus. In the same button/selector configuration flyout, find the “AF Shutter” option
From there, make sure that the “AF-S” mode is set to “Off”, as shown below:
If you want AF-S and AF-C modes not to trigger autofocus when you press the trigger halfway through, you can also set the second “AF-C” option to “Off”.
AF-ON Nikon button
If you’re using a Nikon DSLR or a Mirrorless, you first need to decide whether to use the AF-ON button combination and press the trigger button halfway to get the focus, or use the AF ON button exclusively to get the focus (rear button focus).
After you make this decision, navigate to the custom settings menu of the -> AutoFocus and find the menu setting named “AF Activation.” Within this menu, you will find two options “Shutter / AF-ON” and “AF-ON only”. Choose the second “AF-ON only” option to decouple the focus from the shutter release button to the AF-ON button exclusively.
If your camera doesn’t have a dedicated AF-ON button, see my article on nikon’s AE-L/AF-L button for details on how to set up the rear button focus.
If you want to keep pressing the trigger halfway to focus, but prefer to customize the behavior of the AF-ON button so that it performs some other function, you can change its behavior in the camera menu.
On Nikon DSLR and Mirrorless cameras, navigate to the custom settings menu -> Controls and find the menu option called “AF-ON button”. The opening of this menu should show the following selections:
As you can see, you can change the behavior of the AF-ON button in several ways. You can use it to reset the focus point to the center position, lock focus, or lock exposure in different ways.
Af-ON Panasonic button
If you use a Panasonic Camera, navigate to the custom settings menu and find the menu option called “AF Shutter”:
Be sure to turn it off so that auto focus does not engage. Also, be sure to turn off the “Shutter”.
Then navigate to Operation 1 and select “Fn Button Set”. From there, click the “AF-ON” selection button and make sure that “AF-ON” is selected from the menu:
This will configure the camera to focus the back button.
AF-ON Sony button
With Sony’s Alpha Series Mirrorless Cameras, you’ll need to go through a similar two-step process. First, you’ll need to uncouple the focus from the shutter release button. Navigate to the AF flyout and find a menu option called “AF with shutter”:
Be sure to turn it off. Second, navigate to the “Custom Key” flyout and find the “AF-ON button” option. Set it to “AF On” so that the button engages autofocus, as shown below:
This will configure the camera to focus the back button. If you want to continue pressing the shutter release button halfway down to focus and prefer to change the default behavior of the AF ON button, just choose some other option from the menu here.
I keep the camera AF set only on the AF-ON button and start that way for most assignments. Overall, it’s a setup for fast performance. However, the camera now looks more personalized and the autofocus settings are more intuitive, which is important not just for sports. If you’re messing with camera settings in front of an object, you’re less involved and more likely to miss an opportunity.
Photographers are always looking for techniques that help make great photos. The focus of the back button is a professional detail that caters on various levels. For the photographer ready to step up his game, it is a technique worth investigating
If you have any questions about the AF-ON button, ask me in the comments section below.