Canon EOS-1D X Mark III EOS-1DX Mark III Advanced User Guide - Page 200

E-TTL Balance You can set your preferred appearance (balance) for flash shots. This setting enables you to adjust the ratio of ambient light to Speedlite light output. Set the balance to [Ambience priority] to lower the proportion of flash output and uses ambient light to produce lifelike shots with a natural mood. Especially useful when shooting dark scenes (indoors, for example). After switching to < > mode, consider setting [Flash sync. speed in Av mode] in [ : External Speedlite control] to [Auto] and using slow-sync shooting. Set the balance to [Flash priority] to make the flash the main source of light. Useful for reducing shadows on subjects and in the background from ambient light. Caution Although [Ambience priority] is effective in dark scenes, there may be no difference from results with [Standard] in some scenes. 200