Canon Speedlite ST-E10 Advanced User's Manual page 52

7.
Set the flash output.
8.
Take the picture.
Note
Specify A, B, or C as the receiver firing group when using [Fire all (no separate
control)]. Flash firing will not fire if set to D or E.
To fire multiple receivers at the same flash output level, select [Fire all (no
separate control)] in step 5.
MULTI: Stroboscopic Flash
Using stroboscopic flash at low shutter speeds enables you to capture continuous
movement in a single shot.
For stroboscopic flash, set the flash output, flash count, and flash frequency (flash count per
second, equivalent to Hz). For details on the maximum continuous flash count, see
"Maximum continuous flash
After setting the output, select [OK].
Repeat steps 3 and 4 to set the flash output of all groups.
Each group fires at the set flash output.
count."
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