Hi, gentlemen. Copied this from the Canon PDF guide. When you are shooting individual subjects you want to be set to option 1: ‘Continuous AF track priority.
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With Custom Function C.Fn III-4 ‘AF tracking method,’ the default setting is option 0: ‘Main focus point priority.’ However, when actually shooting with AI Servo AF, there are many situations where option 1: ‘Continuous AF track priority’ is appropriate. So, what type of situation is appropriate for the Main focus point priority setting? With the Main focus point priority option selected, when a subject other than the primary subject moves into the area of the manually selected AF point (usually in the center of the expanded area so it is called the main focus point), you can specify whether the focus should switch to the secondary subject. With characteristics like this, by continuing to take advantage of area expansion (athletes in sports), ‘Main focus point priority’ is effective when you want to continuously switch between targeted subjects. At track events, when you want to switch the focus to an athlete that comes into the foreground, or when you want to continuously switch focus between cyclists in a bicycle road race, this setting can be highly effective.
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Use C.Fn III-8 ‘AF Expansion with selected point’ as described on the previous page, and when shooting extremely fast moving subjects, another important Custom Function is C.Fn III 1-4 ‘AI Servo AF tracking method’ (hereafter tracking method). Basically, when you want to track one subject using area expansion, it is best to set the tracking method to option 1: ‘Continuous AF track priority’ (hereafter continuous priority). When shooting with area expansion and using this setting, if another subject comes into the foreground, it will be treated as an obstruction by the manually selected AF point (the center of the area expansion). Results of focusing are used to detect the position of the subject, and AF points switch from one to the next within the expanded AF points to capture the subject. With shooting situations like this, when using area expansion to shoot moving subjects, the continuous priority setting is effective in almost every situation. When there is no specific target, as we will introduce on the next page, it is probably best to remember, if area expansion is used, use C.Fn III-4 option 1: ‘Continuous AF track priority.’
