Stationary/Still Autofocus Mode
|Stationary/Still Autofocus Mode (Canon 5D)|
In this mode, the camera will focus on the subject and then lock the focus in place as long as you continue to hold the shutter button half way down. The focus will not change after a lock has been achieved. This mode is ideal for subjects that do not move. Most cameras also have several autofocus points in the viewfinder in addition to the center point. If the subject is not in the center, you can select one of the other autofocus points instead. Or you can use the focus and recompose method to focus. For this technique, you first lock the focus on the subject, and then recompose the frame before taking the shot. There is actually a little bit of inaccuracy when using the focus and recompose technique, but it is usually minor unless you are shooting with a very shallow depth of field.
Continuous Autofocus Mode
|Continuous Autofocus Mode (Nikon D300)|
In this mode, the camera will focus on the subject and continuously adjust the focus to keep the subject sharp. Clearly this is the mode to use for things that move. On most cameras, you have a choice on whether you use just a single specified point for focusing, or have the camera track the subject as it moves around in the frame. If you select the tracking option, the camera will automatically activate different points in order to follow the subject. The tracking feature is very useful for shooting things like sports where you are constantly reframing the shot as the action changes. But if you know where in the frame you want the subject, the single point mode will work just fine.
These are the two primary autofocus modes that you'll find on a camera, but there is also a manual focus mode that we should not forget about. The autofocus system in a camera is not perfect. Most of the time it works well, but there will be times when the camera just can't focus on its own. For these instances, you will have put the camera into manual mode and focus it yourself.
There are a lot more focusing options on a DSLR compared to a point and shoot camera. Choosing the right mode could make the difference between an outstanding shot and one that goes into the recycle bin. If you keep the concepts above in mind, you will minimize the number of out of focus shots and hopefully take some pretty stunning photos.