Photography for Beginners Part 27: Back Button Focus

Each post in this series builds on information discussed in previous posts. See the Photography for Beginners page on the menu for links to all the posts.
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Back button focus (BBF) is an autofocus method that uses a button on the back of the camera body to tell the lens to focus, rather than the usual method of half-pressing the shutter button.

Once you are comfortable with using a camera it’s a good idea to set it up to give BBF a try. It takes some getting used to and you need some time to develop new muscle memory, so you’ll want to try it out over several shooting sessions before you decide if it’s for you or not.

If you end up not liking BBF after giving it a fair chance you can reset your camera and go back to the default method of half-pressing the shutter button to autofocus. Many photographers feel BBF is the only way to shoot and once they start using it never go back.

I’m not sure how common people like me are, but I use BBF situationally. It depends on what I’m doing and sometimes just my mood.

Why Use BBF?

BBF is useful because it separates the act of focusing from the act of capturing the image. You decouple autofocus from the shutter button so that the shutter button only takes the photo. Focusing only happens when you press the focusing button.

At first this may sound less efficient because it’s adding an extra step. You first press the button to focus, then the shutter button to snap the pic.

But the beauty of it is that using BBF locks in your focus without having to keep pressing a button and without having to use manual focus. (The one exception to not holding the button is when tracking a moving target.)

Once you experience how BBF works you’ll probably see that it can make things easier and can save you from some frustrations.

Here are some ways BBF can be helpful:

*  The back button is usually easier to use. Some shutter buttons are “squishy” and it’s tricky to reliably hit and hold the half-press position every time.

*  There’s no chance of a failed autofocus attempt after you’ve achieved sharp focus. AF isn’t 100% reliable. If you’re shooting on a tripod there’s no purpose to refocusing for every shot and risking a miss. With BBF you only need to achieve sharp focus once, then take images at your leisure as the light or conditions change.

*  Sometimes timing is critical. With BBF you can pre-focus on your subject and then wait for the right moment like a good facial expression, dance pose, or wave action around a rock before pushing the shutter button.

*  In street and action photography a frequent trick is to zone focus on a specific spot and then wait for an event to happen there, such as a pedestrian walking through a beam of light or a skateboarder catching air. This is can be achieved by using manual focus. But if you aren’t good at or don’t like using MF, using BBF to pre-focus the zone means you can catch the action at the spot you’ve chosen without risking sluggish or missed AF.

*  Focus and Recompose is much easier with BBF because you don’t have to hold a half-press between focusing and recomposing. My finger has a tendency to slip or fail to maintain the right pressure, which means going through the process two or three times for one shot. Or sometimes I accidentally take the shot while I’m still moving the camera. BBF eliminates all those issues.

*  BBF is helpful in any situation in which you want to use AF but don’t want or need the lens to refocus for every shot.

How Does BBF Work?

Some cameras (mostly compact point and shoots) don’t have the button needed for BBF, but most cameras do.

Which button you have available depends on your camera model. You might have a single AEL/AFL button (auto exposure lock/autofocus lock), two separate AEL and AFL buttons, an AF-On button, or some combination.

Cameras that have a lot of customizable buttons may allow you to set a button for focusing other than the buttons mentioned above. If that’s the case and there’s a different button that feels more natural to you go ahead and use it, even if it’s on the top or front instead of the back of the body.

You will need to read your camera manual or look for blog posts or YouTube videos for your camera model to learn the details of how to set the buttons in the menus. There may be some variation between brands of the exact setup and terms used.

For most cameras there are three things you need to do:

1. In the menu set your chosen BBF button to AF-ON. Once you set that, every time you push the button the lens will autofocus. Focus will not change until you push the button again as long as you also do the next step.

2. In the menu set SHUTTER AF to OFF. Doing this is what decouples focusing from the shutter button and tells the camera not to autofocus when you press it.

3. Set the autofocus mode to CONTINUOUS.

Now your camera is set for BBF. How you use BBF depends on what and how you are shooting.

*  Focus and Recompose: use the center AF point on your subject, push the focus button until you see the focus achieved indicator, release the button, recompose, push the shutter button to capture the image.

On a tripod: move your AF point to the spot in the frame where you want to focus, press and release the focus button, press the shutter button with the timer delay on or use a remote release.

Pre-focusing: use the center AF point to focus on your chosen spot or subject, press and release the focus button, wait for the action, push the shutter button.

Moving subjects: use your AF point on the subject, press and hold the focus button, use the shutter button to fire in burst mode. As long as you keep holding the focus button while you’re shooting autofocus should track your moving subject.

Notice that setting up your camera this way means that you never have to switch between single shot autofocus and continuous autofocus. Both are available at all times and it’s how you use the focus button (push and release vs. holding it down) that dictates how the focusing behaves.

This is enough to get going, and is likely all you need to do. However, some cameras offer slight variations in addition to the above to fine-tune how you like to use the camera. What alternatives, if any, are available depends on brand and model.

If you find that you like the idea of BBF but wish the camera behaved a bit differently do a web search for photography forum discussions on BBF for your specific model to see if there are additional options.

Hybrid BBF

One variation that I will mention here is what I use with my Fujifilm X-T20. I call it hybrid BBF.

On my camera I have a back button set to AF-ON. But I did not turn SHUTTER AF off. This means I did not decouple AF from my shutter button.

When my camera is in single shot or continuous AF my shutter button behaves normally, focusing with a half-press of the shutter button.

When my camera is in manual focus mode pushing the back focus button still autofocuses the lens even though the switch is set to manual. And because it’s in MF mode, pushing the shutter button doesn’t make the lens refocus. The camera behaves like any camera set up for BBF.

This way I can quickly change between shutter button focus and BBF with a simple flip of the focus mode switch. I have easy access to both methods without having to go into the menu to change the shutter button functionality.

Most people tend to have a strong preference for either half-press shutter button focus or BBF. But if you’re like me and like to switch between the two you can investigate if your camera will behave this way.

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