The AF point expansion is one of the trickiest focus point selection on the Canon 7D. It’s for the AI Servo mode.
- The AF point expansion starts in the regular single AF point.
- As long as there’s enough contrast/detail at that point, the focus will stay there.
- If the selected point loses the contrast/detail, the Canon 7D will interrogate the points immediately around it. Do you have it? Yes/No, then switch to the next focus point that answered yes.
You cannot control how many expansion points can be used, maximum of 4. The AF expansion points can be used on the 19 points, but at the edges, the AF point expansion will lose one direction. Instead of having 4 different expansion points around the current focus point, it will only have 3 expansion points.
- It’s good for fast moving subject, especially erratic ones
- It’s also good for moving objects that lose the contrast/details at the current focus point like uniforms of football/hockey players or cars…