What Is Autofocus? And How It Works
Autofocus will adjust the lens of your camera to focus on the subject you're photographing to ensure it's sharp.
When you're using autofocus you can use single-shot autofocus or continuous autofocus. Single-shot autofocus is for objects/subjects that are still. When you partially press the button that takes the photograph (shutter button) autofocus will lock onto your subject and stay focused on them. Then press the shutter button all the way down to take a sharp, in focus photo. This happens as half pressing the shutter ensured that focus was locked before you took the photograph.
If you're trying to capture a moving subject, single-shot autofocus doesn't work so you should opt for continuous autofocus. This mode allows the focus to continuously change, which means you can track a subject or object that's moving. On the Nikon 1 V2 camera, for example, it can deliver full-resolution images at up to 15 fps. Or focus on one spot and capture full-resolution images at up to 60 fps
Continuous autofocus works by predicting where the subject will be slightly before it gets there so when you press the button to take the photograph, the camera is already focused on the right place.
You can also try pre-focusing on a spot you know your subject, say a car on a track, will move through. You will need to lock your focus after you've set it up and be ready to hit the shutter button when your subject moves into frame. Just remember to take shutter lag into consideration so you don't end up with an empty scene. What's shutter lag? Well it's the time delay that occurs from when you press the shutter button to when the photo is actually recorded. The lag time will differ on all camera models but no matter what model you use, it usually means you have hit the shutter button slightly before your moving subject comes into frame, giving the camera time to catch up before your subject is in the correct spot.
When shooting fast movement, having a camera with a fast autofocus system will help you ensure your subject is always in focus.
Sometimes when you take a photo where your subject is off-centre it can confuse your camera and it will focus on the background rather than your subject and as a result, you end up with a lovely sharp background but you can't see your subject because they're blurred. However, there is a way to fix this and it's with focus lock.
This means you half press the shutter button while pointing the camera at your subject then with the shutter button still half pressed, adjust the camera's position so your subject is now off-centre then fully press the shutter button to take your shot.
Focusing in most modern cameras works by using a number of sensors. The more advanced the camera, the more AF sensors there are available.
For more control, select a single auto-focus point – many experienced photographers focus just using the central focusing point.
For portraits, make the most of face recognition mode. This is where the camera finds a face in the scene and automatically focuses, adjusts the flash output and optimises exposure. It's useful for when you want to focus on someone in a group, are photographing someone from a distance or are trying to capture a person while they're moving.