EOS

[jrhoffman75]

I assume you know this, but:

1. A camera can only focus at one distance at a time

2. The Canon AF system selects the focus point based on the closest item covered by a focus point with sufficient contrast to activate the phase detection system.

3. AF Expansion starts with the selected focus point first and then looks to the expansion points if the primary point cannot achieve focus.

4. Zone AF has no preferential focus point and will simply select the point that latches on the closest subject with sufficient contrast using any of the focus points in the zone.

[Waddizzle]

Zone AF does not have to select it’s starting point.  

You can select a starting AF point for Zone AF Tracking when in AI Servo mode.

[jrhoffman75]

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@Waddizzle wrote:

Zone AF does not have to select it’s starting point.  

Exactly. As I said above, but explained in more detail:

https://support.usa.canon.com/kb/index?page=content&id=ART133839

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