Making light work
How to make the most out of multiple Canon Speedlite flashguns
All EOS cameras with a hotshoe can be used with the optical or radio wireless flash systems to control more than one off-camera flash. You will need some device on the camera to control any Speedlites that are not directly connected.
Many of the APS-C cameras can use the built-in flash to control remote flashes using the optical wireless system. The pop-up flash sends commands to the remote flashes, but doesn’t have to be used as part of the picture. Or, you’ll need a Speedlite trigger in the form of a Speedlite 550EX, 580EX, 580EX II, 600EX-RT or 600EX II-RT to optically trigger remote flashes. Canon’s radio wireless system requires a radio trigger on the camera hotshoe. The Speedlite Transmitter ST-E3-RT, or Speedlite 600EX-RT / 600EX II-RT or 430EX III-RT flash can work as a radio trigger to control remote radio wireless flashes.
From the camera menus or the unit on the hotshoe – called a sender or master – you can choose to control the remote flashes automatically or set the power level manually. Remote flashes, receivers or slaves, need to be assigned to a flash group. You can have up to three flash groups with optical wireless, and up to five groups for radio wireless.
Working with multiple lights might appear to be a big step, but is actually quite simple, even with automatic flash exposure. First you need to determine how to control the flashes; all automatically with E-TTL mode; manually set power levels with manual mode; or a mix of modes using group mode. With two groups of flashes lighting your subject, you can select a ratio for the lights, and the camera will work it all out for you using E-TTL flash. For consistency, or when lights are aimed back at the camera, manual mode is a better choice.
It takes some button pressing skills and familiarity to be fully effective, but regular practice will hone your skills. I usually have group A for the main light, with group B as the background or light from behind the subject. Multiple Speedlites may be in the same group for extra power. For complex lighting, additional groups are used when needed for the subject.