Canon Speedlite ST-E10 Advanced User's Manual page 37

High-Speed Synchronization
High-speed sync enables flash photography at all shutter speeds. This is effective when you
want to shoot in the aperture-priority AE <
in locations such as outdoors in daylight.
1.
Press the <
2.
Select [Shutter synchronization].
3.
Select [High-speed synchronization].
> button.
Select [High-speed synchronization] and then [OK].
Before shooting, confirm that <
> mode (open aperture) with background blur
> appears on the camera screen.
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