Hi James, Yes, the 550EX uses the main flash tube to send the wireless E-TTL control signals.
The only alternative is to use the ST-E2, which uses a filtered red emitter, but with less range and angle of coverage. Cheers Julian Loke * **** ******* *********************************************************** * For list instructions, including unsubscribe, see: * http://www.a1.nl/phomepag/markerink/eos_list.htm ***********************************************************
