Focusing, Making The Right Thing Sharp
In the majority of portraiture, the subject’s eyes are the main focus of the shot, and it’s therefore important to ensure they are sharp, especially when using a wide aperture. By default, your camera’s autofocus system will usually focus on whatever is in the centre of the frame, or closest to the camera. As a result, when your subject is positioned off-centre or behind foreground elements, you will end up with a blurred subject if you rely on the default focus settings. Even when your subject is in the middle of the frame, you may still end up with your subject’s nose or ears as the sharpest point, rather than their eyes.
To avoid this, you need to manually select which part of the frame the camera uses to set the focus from. DSLRs have anything from a handful of focus points up to 50 of them – with your eye to the viewfinder, use the arrow keys on the back of the camera to select one which covers the area of the frame where your subject’s eye is, then take the shot.
Alternatively, you can leave the focus selection on the central point, position the camera so that this point is on your subject’s nearest eye, press the shutter button halfway down, then re-frame your shot so the composition is how you intended.
Remember that some metering modes are biased towards the area of the frame that’s in focus, so use the Automatic Exposure Lock (a button marked ‘AE-L’) if you want to meter from a different part of the scene to your selected focus point.
Depth of field
Differential focusing is the creative use of focus to intentionally blur the main or secondary subject of your portrait. For instance, you may want the background blurred behind your subject to provide separation and stop it distracting. In a group portrait, you may want just the children to be sharp while the parents are out of focus behind them. Alternatively, you may want to focus on some foreground foliage, while your couple become a blurred silhouette behind it. The depth of field in an image is the amount of depth in front of and behind the focus point that is also sharp. If using a wide aperture, the depth of field could be as shallow as 1cm, which makes accurate focusing essential – any slight movement of the subject or camera after focusing could mean the subject’s eye isn’t pin sharp anymore.
Sometimes the camera’s autofocus can whir back and forth, ‘hunting’ for something to focus on. This can be caused by low light levels, low contrast in a scene, or due to obstacles in the foreground (e.g. a wire fence in front of your subject). In these situations, you may want to switch to manual focus, by flicking the switch near the lens. When you are ready to take your shot, look through the viewfinder and turn the focusing ring on the lens until the subject’s eye looks sharp.
If you are photographing a child running towards you, the time between the camera focusing on them and taking the shot may be enough that the child is out of focus again, particularly if you are using a wide aperture. There are two ways to counter this. The first is to pre-focus on an object that is the same distance from the camera as the child will be by the time you want to take the shot. The second option is to use your camera’s continuous focus setting, which means the camera will track the subject’s movement right up until the shot is captured.