I just got a Canon 430EX (yay christmas!) and it works perfectly when it's on camera (Canon EOS Rebel) but do I need to have another speedlite to do the slave function? I noticed that a friend of mine just needed the built in flash on his camera to trigger his Nikon speedlite (he owns a D80), but when I try to use the built in flash on my Rebel the 430ex doesn't fire. Does the Rebel not support the slave function? EDIT: And if it doesn't, are there any other wireless transmitters I can get that aren't as expensive at the Canon one?