Setting the A:B Flash Ratio
The flash ratio between receiver A and receiver B can be set to specify the main flash and fill flash. The flash ration can be set from 8:1 to 1 and from 1 to 1:8 in half-stop increments. In terms of exposure stops, it ranges from 3:1 to 1 and from 1 to 1:3. When the flash ratio is set, E-TTL autoflash metering controls the flash output to obtain a correct exposure.

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Check that the ST-E2's main switch is set to ON then press the <RATIO> button
- The flash ratio control lamp lights in red and the respective flash ratio indicator lights. The flash ratio for the unmarked indicators are shown in parentheses below

Press the button to select the desired flash ratio
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