Canon SPEEDLITE EL-1 Advanced User's Manual page 100

Flash C.Fn Settings
You can set Custom Functions for the flash from the camera's menu screen. The details
displayed vary by the camera used. If C.Fn-21 to 23 are not displayed, set them by
operating the Speedlite. For custom functions, refer to "Settings that can be changed with
Custom Functions".
1.
Select [Flash C.Fn settings].
Select [Flash C.Fn settings] or [External flash C.Fn setting].
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