The usual way to focus a lens is to press the shutter release half-way down, but many cameras also have an AF button that can be pressed without the risk of pressing it beyond half-way and accidentally taking a few shots.
It is especially useful when using this back-button focus technique to photograph moving subjects that you press the AF button without locking the exposure settings until the point at which you want to take the image and press the shutter release home.
This camera focusing technique allows you to see the subject sharp in the frame and only take the shot when the composition or lighting is just right.
It also means that if something moves into the frame, another player when shooting sport for example, you can stop the focus from being adjusted by taking your thumb off the AF button, but continue to take photographs.
Back-button focusing is also useful when photographing subjects such as plants and flowers that move about a little in the breeze.
If the shutter button doesn’t control autofocus the camera won’t waste time attempting to focus every time the shutter release is pressed and you can wait until the subject is in the right position to take the shot.
Hyperfocal distance focusing
This is a popular camera focusing technique that is designed to get the maximum amount of a scene sharp at any given aperture.
The traditional way of using it is to focus on the subject and then use the lens’ depth of field scale (or a tape measure and depth of field tables) to find out where the nearest acceptably sharp point is.
This point, where the depth of field starts in front of the focus point, is known as the hyperfocal point.
Once the hyperfocal point is found/calculated, the lens is refocused to it so that the subject remains sharp and greater use is made of the depth of field.
The popularity of zoom lenses and consequent loss of depth of field scales has made it harder to apply this technique precisely, but you can still measure or estimate the focus distance and use smartphone apps such as DOF Master to tell you the hyperfocal distance.
Alternatively, you can rely on the principle that depth of field extends roughly twice as far behind the point of focus as it does in front and focus approximately one third of the way into the scene.
Hyperfocal distance focusing is popular in landscape photography and whenever you need lots of depth of field.
This is a digital technique in which several images taken with different focus distances are combined into one image that is sharp from the foreground all the way through the background.
Although it can be applied to landscape photography, it is especially useful for macro photography because depth of field is very limited when subjects are extremely close.
With the camera firmly mounted on a tripod, take the first shot with the nearest part of the scene in focus. Then, without moving the camera, refocus just a little further into the scene and take the second shot before focusing further in again.
Repeat this until you have a shot with the focus on the furthest part of the scene.
Now all the shots can be combined to create one image that is sharp throughout. This can be done manually using any image editing software that supports layers – Photoshop Elements is fine.
But it can also be done automatically using software like Combine ZM, which is free to download and use, or using Photoshop’s Photo Merge function.
PAGE 1: Manual Focus, Single AF, Continuous AF
PAGE 2: Automatic focus point selection, Manual focus point selection
PAGE 3: Face Detection AF, Focus and re-compose technique
PAGE 4: Back button focusing, Hyperfocal distance focusing, Focus stacking