I'm glad I found this beginners area to ask questions because I'm really keen on learning, but have some basic questions. I have a T3 and just bought a 580EX. I was told I could use the 580 as a wireless slave flash with only my built-in T3 flash as the master. Is this true? Because when I try to go into the external flash controls on my T3, it says flash is not compatible or flash is turned off. Do I need another 580 mounted on the camera to act as the master? Or what am i doing wrong?