How accurately you focus an image can make or break the image, sometimes the moment is over as soon as it has begun thus preventing a second, more precise, shot. Today’s auto focus cameras are quite quick and accurate but the photographer must know how to use the cameras focusing system correctly.
Most auto focus cameras use the central point of the viewfinder as the point of focus. Everything else in the image is ignored. Modern advanced camera often have multi-zone focusing. Even with these extra focusing areas, unless you change the focusing area the central area of the viewfinder would still be the default area set the cameras.
Single point systems are always read from the centre of the viewfinder (indicated in red on fig 1). Fig 1 also shows the areas that may be read by an multi-zone auto focusing system. The points marked in blue are a multi-zone focusing pattern alternative. Your camera may differ in the layout and number of areas.
There are various methods to focusing depending on the type of subject being photographed. With portrait and animal photography, whether it is man or beast, the most important part of the image to capture sharply is the eyes.
fig 1. Blue areas indicating focus points on viewing screen. .
If the subject’s eyes aren’t sharp, it is a serious detriment to the image. With most portrait images the viewer will be directed straight to the eyes of the subject, this is a natural occurrence. Therefore the sharper and clearer the subjects eyes, the better the impact of the image.
Here are two photos that are nearly identical (Fig 2 and Fig 3). 
With single zone cameras for portrait photos you aim the center of the viewfinder at the subject’s eyes when you activate the focusing system. Usually this is performed by half depressing the shutter button. If there is a need to compose the image with the eyes in another part of the frame, the focusing can be locked by holding the shutter button in the halfway position and recomposing before fully depressing the shutter button.
fig 2 In Focus
fig 3 Out of Focus
For multi-zone focusing cameras you can select the focus point area nearest the area to be focussed upon. For portrait photos for example, you would normally turn the camera vertically, placing the subject’s eyes about a third of the way down the frame. Select the focus zone closest to the eyes, and focus, use the focus lock described earlier then recompose and fire.
Multi-zone focusing is very useful if your subject is not dead center. Simply because you can get the composition correct first, and then select the focusing zone you require for your off-center subject without having to move the camera again.
For a more in depth look at focussing techniques with examples please see our Basic Photography Course