This is a function I have decided to have a play with on my camera. Its setup by default with the ONE SHOT mode, which is described in my 40D Field Guide as idea for shooting stationery subjects.
In reality, most of mine move, so I have decided to set my camera to AI Focus AF. This seems to be the best of both worlds, it uses OneShot AF but it the subject moves it switches automatically to AI Servo AF.
AI Servo AF tracks a moving subject constantly and will use a manually selected AF point (if you did one) or automatic focus. I haven’t used this mode before so I am interested to see if it improves the quality of the dance images I get.
How to change the Autofocus mode:
Turn the camera on and press the INFO button on the back – this will show you all the image settings you normally see on the top screen and in the viewfinder screen.
Press the AF-Drive button on the top of the camera
This will change the data on the screen to look like this – the ONE SHOT mode is selected by the red square
(for those paying attention this is the same process as changing the Shooting Modes up to here)
To change the Focus mode you use the Main Dial to move between options
Press INFO again and carry on shooting 🙂