Autofocus Area: Why It Matters
Have you ever tried to get your camera to autofocus on one thing but it insists on focusing on something else? For instance, you might like your camera to focus on the centre of a flower, but it insists on focusing on some leaves behind the flower. Or you're trying to get it to autofocus on someone's face, but it focuses on the tree behind the person instead?
Many beginners (and not-so-beginners) haven't realised that they can take absolute control of what their camera autofocuses on. This handy little article shows you how you can get your camera to focus on what it is you want it to focus on, instead of leaving the autofocus to the camera's whims.
The answer to this lies in your control of the Autofocus Area, sometimes called the AF Area in your camera's menu or manual. The Autofocus Area is the area within your viewfinder or LCD display (the "frame" of your picture) where your camera's autofocus points are located. These points, by default, are all active and if they find something to lock onto, they will focus on that thing. The images below show the Autofocus Area in common brands of DSLR and compact system cameras.
AF Areas for DLSR cameras (left and centre) and mirrorless cameras (right).
By default, all the focus points in this area are active, which means that when you half-press the shutter button, they all activate and start looking for something within that area to focus on. Your camera's autofocus loves bright, contrasty, detailed things, so any focus points that detects this will lock focus -- even if the thing it focuses on is a rock, instead of a face.
So, how do you take control of your camera's Autofocus Area?
Simple -- you deactivate all the focus points bar one. You only ever need one focus point to place over a subject to get it in focus.
Have a look at your camera manual and menu, and see how you can change your Autofocus Area to only use a single focus point. Most cameras usually give you a few options to choose from, including:
- Single focus or spot focus - this is the one you want
- Dynamic area focus - useful for focusing on moving subjects (see below for more)
- Auto area focus - this is the one that's selected by default, which means all the focus points in the focus area are active. You don't want to use this.
Have a look at the images below. Each was taken using a single focus point to make sure that I can get my camera to lock focus on the thing I want sharp in the photo - whether it's a specific drop of water, or the eye of a person in a portrait.
In this example, a single focus point is use to ensure a specific raindrop on a leaf is in focus.
Here, a single focus point is used to focus on one of the eyes of the boy in this portrait.
Dynamic Area Autofocus / AF Point Expansion
Many cameras allow you to expand the range of your autofocus to a limited number of points around your selected focus point. For instance, you might choose to use one focus point but dynamic area focus also potentially activates four or eight focus points around your selected point. Dynamic Area Autofocus (called AF Point Expansion on Canon DSLRs) is used when shooting moving subjects in Continuous Focus (or AI-Servo if you are a Canon DSLR user) mode.
The Dynamic Area Autofocus (AF Point Expansion) options for Canon (left) and Nikon (right) DSLRs.
What happens is that you still use a single focus point to lock focus on your subject. But, your subject is moving and you may find it difficult to keep that single point on the moving subject. If your subject happens to move off your selected focus point, then one of the four or eight points around it can pick up on the subject and continue focusing on it, giving you time to move your camera with the subject to keep it in focus.
In the photograph below, Dynamic Area Auto Focus was used to keep the body surfer in focus as he surfed the wave towards the beach.
Dynamic Area Autofocus used to track focus on a moving subject - a body surfer.
If you're still letting your camera choose what it's going to autofocus on for you, then you're missing out on a very significant aspect of camera craft and photography. Take control of your camera's autofocus and you'll never look back!