@HenryTS wrote:
From the 550EX users manual I understand how to adjust the ratio between slave speedlights with the master turned off, but how do you adjust the ratio between the master which is turned on and a slave?
Put the master and the slave in different groups. (master in Group A, and slave in Group B)
Speedlite Tip Series, Part 3: Wireless Flash Primer
The master flash unit is always in Group A. Slave units can be assigned to Group A, B, or C via the control menu on the slave unit’s LCD pane
