It’s time to take focus to a whole new level with Back Button Focus. This simple menu change provides a great technique for creating sharper images while eliminating the hassles inherent in shutter activated focusing. I am not sure that every camera manufacture offers this function so please refer to your particular camera manual.
If you have not read parts 1, 2, and 3 of this blog series, I encourage you to take a few minutes and do so by clicking on the following links: Photography Guide to Sharper Photos- Part 1 , Photography Guide to Sharper Images- Part 2, Photography Guide to Sharper Photos – Part 3. Basic focusing functions were covered in depth in those posts.
Since this is a post about sharp images, please be sure to click on each image as the thumbsnails in WordPress posts never appear that sharp. This drives me nuts!
What is Back Button Focus?
Back button focus simply removes the focus function from the shutter button and assigns it to a different button. By default, the shutter button is designed to open the shutter and manage both exposure and focus; all with one touch. Therefore, when the shutter button is pressed, autofocus occurs. Back button focus is nothing more than using a different camera button to activate autofocus.
Some people get confused and think that back button focus and back focus are the same. That is not true, Back focus is when the lens focus is behind a subject instead of on an intended subject.
Benefits of Back Button Focus:
- Focus stays constant -When focus is tied to the shutter button, every time the shutter button is no longer activated, the camera stops focusing on the subject. With back button focus, the camera maintains focus on an area even after your finger is off the button. Here are a couple examples on how this feature helped me recompose images in the field.
A red shouldered hawk
With back button focus I was able to focus on the bird once then recompose the image without having to keep the shutter depressed until I was satisfied with the composition. For this image, I placed the center focus button around the eyes of the bird than recomposed the image to move the hawk out of the center of the image. I did not have to keep a button depressed or refocus the bird.
Entrance to Wormsloe Plantation
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In this image of the entrance to Wormsloe Plantation in Savannah, Georgia, I decided it would be wise to use a cross type focus point to ensure the most accurate focus. After focusing, I was not completely satisfied with my composition since it was made using the location of only the camera’s cross focus points. In the initial composition the top portion of the trees were in bright light that detracted from the rest of the image. So I decided to move my camera down slightly to remove the top bright portion of the trees. Here again, focus remained where I originally placed the focus point and there was no need to refocus the image.
- Freedom to select the most accurate focus point– In the past when focus was tied to the shutter button, I had to focus and keep holding the shutter button halfway down while I composed or I had to press the AE button to lock focus. To shorten the length of time to recompose an image, I would sometimes select the focus point that gave me the best composition instead of the most accurate focus point. Remember from my earlier posts, not all focus points are equal.
- Unexpected movement will not alter the focus -With shutter activated focus if anything enters the focus area while the shutter is being pressed, the area of focus could move to that new object. With the back button focus, once it is set, the focus will not move unless you press the button again or continue to hold the button down.
One thing to be aware of is that focus will be accurate only as long as the distance between photographer and subject remain constant. This is true regardless if focus is tied to the shutter or a different button. In other words don’t focus then walk back 10 feet and expect everything to stay sharp.
- Switching between focus modes is simple-There is no longer a need to change a setting on top to the camera from AI Servo/AFC to One Shot/AFS if you wish to change modes. With back button focus, I keep my camera in Al/Servo (a Canon focus mode designed for moving subjects). To photograph a moving subject, I simply keep my finger on the back focus button while pressing the shutter. For stationary subjects, I focus and take my finger off the button. This is by far my favorite feature of Back Button Focus.
Fast Moving Pronghorns
In the above image, since the pronghorns were running, I kept the back focus button depressed until the shutter was released. Remember if you take your finger off the button, focus will stay in it’s original location. In this example, the pronghorns would have moved way past the focus point.
Above is another example of a fast moving subject that required the back focus button to be continuously depressed.
Yes moving subjects still require the photographer to continuously press a button for focus the same as when the shutter controlled the focus. However, unless you photograph only moving subjects, there are still benefits to back button focus.
Why change focus modes?
If you noticed, I mentioned that I sometimes change focus modes. And yes, many photographers recommend always photographing in AI Servo/AFC. Well I agree with this most of the time but not always. About 90 percent of the time (prior to using back button focus), I photographed in Al Servo (Canon)/AFC (Nikon) mode. However there were times I did not want to risk an area of focus being impacted by a moving subject. In those situations, I photographed in One Shoot/AFS mode.
Let me share with you a story. Years ago, I was photographing a church steeple in Charleston, South Carolina. The steeple had beautiful afternoon light on it and was set against a dark stormy sky. This was a dramatic scene that I could not wait to capture. Well I gleefully shot away only to arrive home and discover that my images were badly out of focus (before Live View). I was perplexed but on closer inspection found the culprit. With the approaching storms, small birds were flying all over the sky in front of the steeple. So guess what happened when the birds flew into the focus area; focus moved from the steeple to the birds. I never even noticed these tiny birds at the time. If I had used back button focus, focus would not have moved to the birds when the shutter was activated.
Let’s take a look at the next image of a white bridge at Magnolia Gardens. With shutter activated focus in AI Servo mode, any movement of the leaves and moss hanging close to the bridge could have altered focus on the bridge if a focus point was near the leaves or moss. This was not a chance I wanted to take so I changed focus mode to One Shot. (Note: even photographing stationary subjects, pay attention the everything in the scene that can move.)
Magnolia Garden’s Famous White Bridge
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Many times after photographing a subject, I would forget to change the setting back to AI Servo. If my next subject had movement, I would end up with a bunch of out of focus movement shots. Now, I don’t have to worry about it. All I have to do is hold the back focus button down for moving subjects and focus and release the button for stationary subjects.
How do I set my camera to Back Button Focus?
Since every camera will be different you will have to refer you to your specific camera manuals. For illustrative purposes and to show how simple it is to change focus from the shutter to another button, here are the steps I follow on one of my Canon cameras.
Canon Steps to Remove Focus from Shutter Button
Select the Custom Controls Menu:
Once you hit OK, you will then see this screen:
Notice in the image above that when focus is set to the shutter button and the shutter is pressed halfway, both metering for exposure and autofocus begin. We are going to change that.
Select the box and this next screen will appear.
Next I changed the camera default from the shutter button with the AF to the orange box with only the shutter button which effectively removed the AF feature from the shutter button. Now when the shutter is pressed only metering for exposure begins.
Next we have to assign the auto focus function to a new button. I have two buttons I can use to AF, one button is called AF-On and the other button simply has a *(AE lock) on it. (As you can see my buttons are worn out from use)
Although I could select either button, for purposes of this example, I will select the AF-On button.
Next I have to tell the button what I want it to do.
I move the orange box to the first choice with the AF by it. With this change I have now made the AF-On button on the back of my camera responsible for focusing.
For Nikon and other camera brand owners, please check your manuals for specific steps to change your auto focus button.
Why I don’t think beginners should use Back Button Focus.
I have taught beginner classes in photography for quite a number of years. In almost every case, students in the classes were photographing in a program mode and therefore unfamiliar with most of the camera controls and buttons. So when I had them photograph in manual mode, most struggled and became frustrated with having to set shutter, aperture, ISO settings and select a focus point. I fear that adding one more button into the mix would only increase frustration levels and send everyone back to an auto mode. That is the last thing I want any photographer to do.
I am a firm believer that every photographer should control their camera settings, not let the camera set the controls. Once students become accustomed to using the camera dials, I introduce the back button focus. For students that continuously struggle with moving the dials, I never mention back button focus. Of course, I know some will disagree with this approach but that’s OK.
So, for you beginners out there, get comfortable moving around your camera controls first, then make the change to back button focus. Shutter focus works well in most situations and you don’t have to move to back button focus until you are ready.
Thanks for joining me again on another Technical Tuesday session (well Thursday in this case) and I hope to see you back in three weeks for a discussion of Depth of Field (DOF) and Hyperfocal Distance. Introduction to Depth of Field Note that due to upcoming travel and an event, I have delayed Technical Tuesday posting for a week.