3. Back Button Focus
Author: Rick Budai from Wild Artistic
What is Back Button Focus?
What are the Advantages to using this technique to acquire focus?
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.