Speedlite 600EX-RT: auto assist beam firing

Within the camera menus of several EOS models, there is an option to enable or disable the AF assist beam when shooting in low light. If you enable the function on the camera menu, but the AF assist beam on your external Speedlite does not fire, check the Speedlite’s custom function settings. If the custom functions in the Speedlite are set to not fire the AF assist beam, this will over-ride any setting made in the camera menu. To re-enable the AF assist beam, simply switch the Speedlite custom function to allow the beam to fire.
Keywords:
EX Speedlites
Flash