[1] Wireless System Setup and Testing
The wireless flash system can be setup in one of two ways: 1 With a 550EX set as the master unit and one or more 550EXs set as slave units. 2 With Speedlite Transmitter
This section describes the procedure for the former. For the latter, refer to "[4] Manual or Stroboscopic Flash With a Slave Unit" on page 110,111.
1. Setting the 550EX as the Master Unit
Attach the 550EX to the camera and set
the wireless selector to 
. This 550EX will then be the “master unit.” The master unit’s wireless signal is transmitted to the slave unit(s) at almost the same time as the shutter release.
The master unit’s flash head zoom setting is set automatically to 
. This gives the
wireless signal the maximum coverage of 80˚. You can also press the 
button to change the zoom setting manually. However, this will narrow the wireless signal’s coverage.
2. Setting the 550EX as a Slave Unit
Set the wireless selector to 
on the 550EX to be used as a slave unit. A 550EX set in this way is called a “slave unit.”
• The slave unit’s flash head zoom setting is
set automatically to 
.
You can change the slave unit’s flash head zoom setting manually with the button.
