I have several small flashes equipped with sensors that cause them to fire as slaves and have a notion of how to synch them with the G5's shutter, uneffected by pre-flash. Please let me know if I'm on the right track --
An ancient, but perfect, Canon Speedlight 177A is clipped onto the camera's bracket and the built-in flash is masked with serveral plies of Post-it Notes to prevent it from emitting its burst. Focus is done manually, shutter speed is set at 1/60 and the 2nd screen is set up. For portraits in shady, exterior settings, ISO 200 is generally used.
Canon "Support" has got me confused because they respond that the G5 won't work with the Speedlight 177A. Wrong! I just tested it on a still life in a darkened room (but did not test the situation with the slaves).
Am I on the right track? Am particularly interested in shooting portraits outdoors in shady locations using the slaves and a silvery reflector. What settings would you use?

