Learn the Terms > Autofocus

Autofocus

Get it right, because focus is hard to fix

If you don't get a digital photograph right, you can always fix it.

There are plenty of image editing programs that will let you resize, adjust exposure, remove red-eye, fix colors and remove spots and blemishes. The one thing that you cannot fix is focus.

If you take a digital photograph out of focus, there is nothing you can do to make it look sharp. Because of this limitation, you want to make sure that your photo is in focus when you take it. Your camera's autofocus will help you.

Focus Points

In older film cameras, there is no such thing as focus points. The cameras focused on whatever was dead center in the viewfinder. This makes adjusting your composition tricky. Say that you don't want the primary subject to be in the center of the photo. With center focus cameras, if you didn't point the center of the camera at them, they would not be in focus. You had to focus on your subject, adjust your composition, and then take the shot.

Today's digital cameras are quite different. Virtually none of them have only one focus point. The standard number is three.

This means that the camera can now focus on three separate points, typically arranged horizontally side by side. If your primary subject is to the left, the camera picks the left focus point. If the subject is to the right, the camera selects that.

This means that you don't always have to point the camera straight at your primary subject to get it in focus.

Think that is helpful? Then think about what it's like to use a camera with nine focus points. These cameras typically arrange their focus points in a grid pattern. It means that no matter where your subject appears in the frame, they will always be in focus.

One-shot and Predictive Autofocus

The large majority of digital cameras only have one-shot autofocus. This is how it works: to focus on a subject, you point the camera at it and push the shutter halfway down. The camera will focus, and will let you know that it is in focus by beeping. When the camera has multiple focus points, it will light up the focus point is has selected for the shot.

Once the camera chirps to let you know the subject is in focus, you push the shutter all the way down and take the photo. When you get ready to take another shot, you have to push the shutter button down halfway again, and wait for the camera to focus.

Predictive autofocus is rare in compact digital cameras, but is a fairly standard feature on most digital SLRs. In this mode, the camera is continuously focusing. You can push the shutter at any time — you don't have to wait for the camera to focus and beep.

Predictive autofocus attempts to determine where the subject is and set the focus accordingly. This is especially helpful when you are taking photos of a moving subject. If you focus on a subject moving toward you, by the time you take the shot the subject will be closer and out of focus. Predictive autofocus tries to determine where the subject will be and sets the focus when you press the shutter button.

Focus Speed

Before you rush out and buy that digital camera you've been wanting, take it for a test drive at your local camera shop. The most important thing to test is how long the camera takes to focus.

Some compact digital cameras (especially older models) take 3 seconds or more to focus. This does not seem like a lot, but when you are trying to capture that critical moment, 3 seconds is an eternity. You can miss a lot of great photo opportunities if your camera can't manage to focus.

This test is not valid when there is not a lot of light. All digital cameras (even digital SLRs) have trouble focusing in low-light conditions. With a digital SLR, you can get around the problem by switching your lens from autofocus to manual focus. With a compact, there is not much you can do — most compacts don't have a manual focus setting.

What to Look For

Most snapshot photographers are going to need one-shot 3-point autofocus. This will cover your everyday shooting situation. Just make sure that the camera can focus fast enough for your tastes.

The avid sports photographer is going to go nuts with one-shot autofocus. With kids at play and pets in motion, few shots will be in focus. If your passion is subjects that are always moving, then consider a camera with more focus points and a predictive autofocus system. You'll wind up with a lot more shots you can keep and less that you throw away due to poor focus.