Back Button Focus | How to be BFF with BBF

You hear about it in photography groups and forums all the time...back button focus. What the heck is it and why in the world do people talk about it like it is the greatest thing of all time? 

I had a hard time wrapping my head around it when I first encountered BBF speak. I kind of sort of maybe understood, but I didn't really "get it". Despite not fully understanding the benefits, I jumped in and started using it and haven't looked back. 

Now-a-days, I understand much more about WHY people (including myself) like it so much and am hoping I can de-mystify the subject a little bit for you as well!! 

how to use back button focus


In the absolute simplest of descriptions, you use a button on the back of your camera (instead of the shutter button) to focus on your subject. 

With most DSLR's right out of the box the shutter button will control two things: the focusing mechanism as well as firing the actual shutter in order to take the photo. 

When you depress the shutter button halfway, the camera will search to find focus based on what focus point you have activated, and then if you continue to depress the button the shutter will fire and the camera will take a photo. 

Setting up your camera to use back button focus means that you separate those two functions into two different buttons. The shutter button will only fire the shot and a button on the back of your camera will attempt to find focus when you press it. 



The easiest way to describe the benefits is through a couple of different examples. 

Example 1: no need to refocus

Let's say you are photographing a dark wedding reception and you are having trouble achieving focus in order to take your shots. You are pressing the shutter halfway, but the camera is hunting and hunting for focus and is having trouble locking due to the low ambient light available. The shutter WILL NOT fire unless focus is achieved meaning you could be missing key shots because your camera will not find focus. 

If you use back button focus however, you can go into a better lit area, stand a certain distance away from a subject you can focus on (lets say 4-5 feet), grab focus and then go back into that dimly lit reception, don't press the focus button and take all the shots you want (as long as you are standing about the same distance from the subject). You don't have to worry about the camera hunting for focus again. The shutter will continue to fire because the camera has already locked in a focus distance. As long as you are 4-5 feet from a subject, your depth of field will remain the same and whatever subjects are that far away from you will be in focus. 

Example 2: focus will stay locked

Have you ever been shooting something and then all of a sudden something else comes in front of the lens? When you press the shutter again to take the shot your camera will attempt to focus on whatever that is, instead of the intended subject and you could potentially lose a shot since you will have to attempt to focus again on what your original subject was. 

If you use back button focus, the focus will remain locked on your subject despite other things getting in the way. Since you won't have to attempt to get focus AGAIN once the photobombing object gets out of the way, you can simply depress the shutter to take the shot instead of having to find focus again. 

Example 3: shutter will fire

Since achieving focus is no longer a function of the shutter button, you will be able to fire the shutter and take a shot whether you have achieved focus or not. 

This can benefit you in a few different ways. You can get creative with some shots and artistically have nothing in perfect focus in the shot. You can grab certain emotions or moments that may not be perfectly focused but if you had waited to grab that perfect focus you might have missed them all together because the shutter wouldn't fire. 

Example 4: tracking your subject

If you are shooting a moving subject, say a bride and groom walking down the aisle towards you, back button focus is awesome. As long as your camera is in AI Servo (for Canon) you can just hold down the back button and the camera will continue to track your subject and maintain focus. You can keep pressing the shutter button and your shots will still be in focus as long as you hold down that button on the back at the same time. Brilliant!



Here are the instructions for Canon 5d Mark iii and Canon 6d. Nikon users, you'll need to do some googling (and maybe some purchasing of new Canon gear?) Just kidding!! ;-)

For a Canon Mark iii

Step 1: Go to your Custom Controls
Step 2: Select the shutter button and change it to "metering start" 
Step 3: Select either the AF-ON button OR the * button (your choice really) and change it to "metering and AF start" 

For a Canon 6d

If I remember correctly with the 6d, out of the box either the AF-ON or * button is already programmed to focus, but the shutter still will be set to do BOTH metering and focus, so you will still need to change that to metering start ONLY. 

Step 1: Go to your Custom Function III : Operation/Other- click set
Step 2: Scroll until you get to 5 which is Custom Controls
Step 2: Select the shutter button and change it to "metering start" 
Step 3: Select either the AF-ON button OR the * button (your choice really) and change it to "metering and AF start" (if it is not already set at that)