The AF-area modes are designed to give you control over how many AF points are in use at one time. These modes offer various ways to track subject movement.
Figure 11-4 shows the AF-area mode selector in the Single-point AF position.
Figure 11-4. AF-area mode selector at Single-point AF
This mode uses a single AF point out of the array of 51 points to acquire good focus. As mentioned before, you can control which AF point is used by selecting it with the Multi Selector. In Figure 11-5, notice that the center AF point (of the 51 sensor points) is the one that provides focus information.
Figure 11-5. Center AF point ...