What is Back Button Focus?
By default, the shutter release button performs two functions. Firstly, you achieve focus by half-pressing the shutter release. Secondly, pressing the shutter release all the way takes the shot. Back button focus, on the other hand, separates these two functions. In other words, the shutter takes the shot while a button on the back tells the camera when to autofocus.
This technique does take some getting used to. Furthermore, not all cameras have this function available. Most modern DSLR’s, however, do allow for back button focusing.
What are the Advantages to using this technique to acquire focus?
The main reason for using this technique is efficiency. What do I mean by that?
There are a couple of good reasons why back button focusing makes sense:
- Allows you to lock and maintain focus. Regardless of how many focus points you have available, the center-most points are the most accurate when trying to focus. The advantage of using this method is that once you remove your finger from the button – Focus is locked. This allows you to recompose your shot without affecting focus.
- Easily switch between single and continuous autofocus. Holding down the button allows you to continue focusing. As long as you keep your subject within the chosen AF points, holding down the button, the camera will continue to focus on the subject whilst tracking. This is particularly helpful when photographing moving subjects such as a bird flying.
- The ability to switch between autofocus and manual focus. Although autofocus has come a long way since the early DSLR’s, it isn’t perfect. Often, the lack of contrast in a scene makes it difficult to acquire focus using autofocus. In this instance, it is important that we have the ability to take control. With the default setting active, pressing the shutter engages the autofocus function. In a low contrast scene, this may prove difficult. At this point, we need to switch over to manual focus. This means either flipping the switch on the lens or navigating through the camera’s menu. Either way, it’s time-consuming and not very efficient. Using the back button, autofocus stops the instant we no longer press the button. This allows us to adjust the lens manually without adjusting any additional settings. This is useful when capturing animals that are camouflaged.
Why back button focus is important in wildlife photography
In the example above, I used the center AF points to acquire focus. With the focus locked, I was then able to recompose and capture the shot.
For this shot of a great white breach I was able to continuously focus in one spot in anticipation of the breach. I combined back button focus with center AF point. In addition, I chose an AF setting which instantly focused on subjects suddenly entering the AF points.
As I mentioned, it takes some time to get used to this method. Practice this technique prior to going on safari. It is an absolute time saver. I highly recommend using this method.
Follow this link for another wildlife photography quick tip – Custom Shooting Modes