AF Modes

The next step is to understand what the various AF modes of your camera do. There are typically three: Single shot, Continuous and Auto (as with most aspects of photography these terms may not be exactly the same on your camera, but they should be reasonably similar.) The AF mode you pick will ultimately be determined by the actions of your subject.

Single shot

This is typically the default mode on most cameras. It is also the simplest of the three modes. When you press the shutter button halfway down the camera focuses and then, once focus is achieved, locks focus and stays locked. The camera will only try to re-focus if you take you finger off the shutter button and press the shutter button down again. For this reason, Single shot is not the one to pick if your subject is liable to move. It is ideal however, for static subjects such as landscape or posed portraiture (though not children, who may get bored and move!). It is also the mode to use for the focus-and-recompose method described above. 

Continuous

If your subject is likely to move then Continuous is the mode to choose. When selected, the camera’s AF system continually adjusts focusing distance to keep your subject sharp. (If the subject is moving, but keeps the same distance from the camera then focus is adjusted less, if at all. It is when the subject is moving closer or away from the camera that Continuous works hardest to maintain focus.) Unlike Single shot, focus is not locked until the very moment that you press fully down on the shutter button to make the photo.

Auto

Auto is basically a hybrid of Single and Continuous. Initially, AF acts as the same way as Single shot if your subject is static – focus locks when you half press the shutter button down. However, if the subject then begins to move, then the AF system will re-start and then essentially act the same as Continuous. Auto is a useful mode if you are unsure whether to choose Single shot or Continuous. However, there can be a slight lag before the camera re-starts AF and this lag may just be enough to miss a photographic opportunity. If your subject is very likely to move use Continuous in preference.