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I am doing some very closeup work with my Rebel xsi. Due to lens shadowing, I need to use a ring flash, connected through the hot shoe. The camera works 100%, as does the ring flash. however, no matter how I set the camera, the flash is not triggered...

I am doing some very closeup photography [jewelry] where I need to use at least 2 detached flash units. I am using the Canon Rebel xsi.Can someone guide this photo newbee to how to use multiple flash units, and what I must look for such that the flas...