Adjusting the flash exposure
Make the flash more obvious or reduce its brightness for more subtle results
Just as you can make a standard exposure brighter or darker using the exposure comp setting, you’re able to use flash exposure comp to increase or decrease the brightness of the subject lit by the flash. E-TTL II flash metering is intelligent, but there’s still a chance that it can be thrown by reflective objects such as mirrors and windows, for example, causing it to make the flash exposure less bright. Or you may just want to reduce the flash exposure so that you only have a subtle amount of fill-flash to lift the shadows in a daylight photo.
You can set the flash exposure comp amount for either a built-in flash or a Speedlite on the Quick Control Screen or in the camera’s Flash Control/external Speedlite Control sub-menu.
Alternatively, you may be able to make the adjustment directly on the Speedlite or Speedlite transmitter that’s attached to the camera’s hotshoe. If flash exposure compensation is set on both the camera and the Speedlite, then the Speedlite setting overrides the camera’s.
More recent EOS bodies such as the EOS R5 and EOS R6 give you an additional control called ‘E-TTL Balance’. You can leave this set to
Standard or choose from two priority modes: Ambience priority or Flash priority. With Ambience priority, the camera reduces the flash output so that the ambient light is the dominant light source. Flash priority does the reverse, making the flash the more obvious main source of light.