Canon EOS-1V HS Instructions Manual page 92

Flash Photography with Speedlite 550EX
Wireless, Multi-Speedlite System
Speedlite 550EX has the following three features:
(1) E-TTL autoflash
(2) Slave unit feature
(3) Master unit feature for wireless control of 550EX slave units
By using the above features, you can set up a wireless E-TTL autoflash
system with multiple Speedlite 550EXs.
You can also set a flash output ratio for up to three groups of Speedlites to
create the desired flash lighting effect.
• For details, see the 550EX and ST-E2's Instructions booklet.
Wireless, multi-Speedlite system
Transmitter
ST-E2
Speedlite 550EX Speedlite 550EX
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