Back-button autofocus—a large number of photographers love it, others have no idea what it is. Most photographers use the shutter to focus. Back-button autofocus is found on many DSLRs. A button on the back of the camera is conveniently located where your right thumb falls when you hold the camera. This button takes over the job of focusing when you set it in the custom menu. Instead of pressing the shutter halfway down to activate autofocus, press your thumb on the back button. The shutter button is still used to make the photo.
There will be an adjustment period before you feel comfortable using back-button autofocus. Most photographers pick up a camera and innately use their pointer finger to acquire focus and release the shutter. Since the thumb will take over the task of focusing, deliberate thought has to be put into the process. The primary reason photographers stick with shutter finger focus is that back-button autofocus doesn’t feel comfortable in the beginning. Given the learning curve, photographers stick with the traditional method and use the shutter. If you dedicate time to adopt it, there are some advantages. I offer the following for you to think about to see if the scenarios fit into your shooting style. If they do and you’re willing to invest the time to get used to back-button autofocus, there are advantages—you make the decision!
Off-Center Subjects: Back-button autofocus allows the photographer to lock focus anywhere in the picture, recompose the shot and then press the shutter to make the picture without having the camera try to refocus. As long as the subject and photographer don’t move, autofocus remains fixed at the locked distance. Traditionally, the photographer can lock focus by pressing the shutter halfway and recomposing the image, but this must be repeated for every picture. An alternative is to move the active focus point over the off-center subject. What method works best for you?
Obstructions: Moving subjects can be a nemesis to autofocus. Since continuous or servo mode autofocus is used for moving subjects, if something gets in the way of the subject, the autofocus system may try to lock onto the obstruction. With back-button autofocus, you can temporarily remove your thumb from the focus button and keep taking photos of the primary subject using the shutter button.
Manual Focus Switch Isn’t Needed: When you’re out in the field, there may be times when you have to use manual focus. For instance, the situation may dictate you don’t want the lens to refocus every time you press the shutter. This involves switching the focus method either on the camera body, the lens, or both. If you use back-button autofocus, you never need to activate these switches because the pressing of the shutter no longer controls focus.
Sports: Lock the focus and wait for the action. Let’s use the example of a baseball game and you have two cameras going. Use your long lens to lock focus on second base for the dramatic double play or slide into the base. Set the long lens body to back-button autofocus and let the action happen right at the base. If the traditional method of shutter release focus is used while you track the subject, the movement of players may fool the autofocus and the entire sequence may be lost. If back-button autofocus is already locked into that point on the base, when the action is peak, focus is guaranteed.
Macro Benefits: Many macro photographers use a method of focusing where they rock back and forth to obtain sharpness. Because depth of field is ultra critical in macro photography, it’s imperative that the focus point is strategically placed. With back-button autofocus, it’s easy to get the focus in the ballpark and then use the rock back and forth method to massage the precise point you want sharp. With the traditional shutter release method, unless you keep the shutter button pressed halfway down, the focus won’t lock.
Back-button autofocus may or may not work out for you, but you won’t know unless you give it a try. You may want to incorporate it for just the circumstances where it makes sense. Certainly, there are times where it’s advantageous, so use it for those times. To set back-button autofocus on your camera, go into the custom menu and navigate to FOCUS. Set it up where you remove focus capability from the shutter and dedicate it to the thumb button on the rear of the camera. If you decide it’s not for you, reset the camera to the traditional method.
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