I have recently switched over to back button autofocus, and wished I would have done it sooner. For me, back button focusing got rid of one of my top annoyances with photography, which is pressing the shutter down halfway to autofocus and then pressing it down completely to get the shot. I didn’t care too much for it, especially when it came to taking multiple photos in a row. The process becomes: Focus, Recompose, and Snap for every shot. With back button focus, you program one of your back buttons to autofocus, and the shutter button is only for snapping the shot. Also, once you achieve focus with back button focusing, your focus is locked into that position. So, if you are taking a portrait and you want to get multiple shots of your subject with different facial expressions, all you have to do is focus once by holding the back button until it focuses, then you can take as many photos as you want without the repeating process of focus, recompose, and snap. When you have a moving subject, make sure change your AF mode to AI Servo.
I am going to show you how to setup back button focus on the Canon 5d Mark III and the Canon T1i. If you don’t have either one of these, it’s OK because theses steps will get you started on the right foot. Also check the owner’s manual for more guidance. For the Nikon users, you can check out this blog from Improve Photography on Back Button Focusing. For the Canon 5d Mark III do the following:
- Go to 2nd Custom functions menu (C.Fn2:Disp./Operation)
- Go into custom controls
- Take autofocus away from the shutter button by scrolling to the shutter button icon and pressing set
- The shutter button is already set on “metering and AF start”. You can change the shutter button to “metering start” or “AE lock”
- Go back to custom controls and select the AF-On button icon (or the AE-Lock button icon)
- Assign the “Metering and AF start” function to this button
For the Canon T1i you can set the controls for the Shutter button and the AE Lock button (*). To change to back button focusing on the T1i:
- Go to the 3rd settings menu and go into “Custom Functions (C.Fn)”
- Go to menu number 10
- Choose either option 1 (AE lock/AF) or 3 (AE/AF, no AE lock) to set the AE Lock button to focus
Keep in mind that if you are taking a photo of a subject in motion, change your AF mode to AI Servo. When shooting a subject in motion (i.e. a child running outside), make sure your AF mode is set on AI Servo, then you have to press the back button and hold the back button to focus on the subject. Continue to hold the back button as you follow the subject with your camera. The focus will stay locked onto the subject as long as you have the back button pressed. So there you have it! No more pressing the shutter down halfway to achieve focus. If you haven’t switched to back button focusing already, give it a try, and see if it makes life easier for you.