For EOS DSLRs
This dedicated E-TTL (II) wireless flash transmitter lets you control an unlimited number of 420EX, 430EX, 550EX and 580EX flashes in two groups. Dedicated controls on the unit allow you to control all slave unit functions, without having to access each flash. Flash output ratio between groups A and B can be adjusted from 8:1 to 1:1 or from 1:1 to 1:8 in half step increments. Other features include an AF assist beam when shooting in low light, and high speed sync compatibility for maximum flexibility in your lighting.