Up until not too long ago, I always relied on half-pressing the shutter to autofocus. Using just the shutter release button is obviously a time-tested way to achieve proper focus in a variety of situations…but after reading an article about using a back-focus button, I figured I’d give it a try. At first I was expecting it to complicate the process of composing a photograph…after all, instead of auto-focus and shutter release being limited to just one button, I would now be using an altogether different button to control autofocus.
Well…after using it for a few weeks, I am surprisingly pleased with the process.
What is back-button focusing? You use a single button on the back of your camera which is fully dedicated to operating the autofocus mechanism, so that focus will be separated from the use of the shutter release button. If you have the camera properly set up for back-button focusing, half-pressing the shutter will no longer control focus. To achieve proper auto-focus, you simply press the dedicated button on the back of the camera.
Don’t confuse back-button focusing with “back-focus”. Back focus is an issue where a lens will focus behind the intended subject. Totally unrelated to back-button focusing.
Some cameras have a dedicated autofocus button on the back of the camera…typically it is labeled “AF-On”. Other cameras require you to re-program the function of a different button on the back of the camera. For example…the Nikon D750 does not have a dedicated autofocus button…so I use the AE-L button as the autofocus button:
To reprogram the button on the Nikon D750, you simply go into the custom controls (Letter F in the Custom Settings Menu) and edit the AE-L button under “Controls” (F4) to be assigned to “AF-ON”. From now on pressing that button will engage the auto focus.
For more detailed instruction on how to re-program your specific camera, check out this article.
You will also want to program the shutter release button so that the camera will take a picture even when focus has not been achieved. To do this on the D750, go into the custom setting menu under “Autofocus”, then select “AF-C” and “AF-S Priority Selection to “release”.
Occasionally, using only the shutter release button to focus was pretty frustrating. For example…suppose you want to lock focus on a subject, then recompose the shot. Once you recompose and press the shutter release again to fire a shot, the darn camera will refocus to the new area it’s targeted on…unless you press the AF-L button to hold focus the whole time you’re re-composing, or switch to totally manual focus.
With back-button focusing, you only need to press the AF-On button a single time to achieve the proper focus, then let the button go, recompose, and press the shutter. The camera will not refocus unless you press the AF-On button again. You are locked on a specific focal length. And, no more accidental out of focus shots because you fully pressed the shutter release when you were only trying to half-press it.
One thing to keep in mind is that, if your camera is set up to back-button focus, you will not be able to control focus while using a remote shutter release. Half-pressing the remote shutter is exactly the same thing as pressing the shutter button on the camera. You would have to adjust focus using the back button first, then use the remote to fire the shutter.
That’s pretty much the basics for back-button autofocus control. Keep in mind that back-button focusing is a totally subjective process…some people swear by it, and others don’t care for it. Give it a try to see if it simplifies the process of getting the image you want.