Canon Speedlite 430EX User Manual page 29

Setting Manual Flash with the Slave Unit
Manual flash can be set manually with the slave unit. Do this in the
following cases:
(1) When you want to set the flash output with the slave units
individually for wireless or manual flash, as with studio flash units.
(2) When you use Speedlite Transmitter ST-E2 for wireless or manual
flash.
Press the <D> button for 2 sec.
<q> will blink.
Set the manual flash output (p.19).
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