Canon EOS R6 Advanced User Guide - Page 165

Shutter synchronization Normally, set this to [First-curtain synchronization] so that the flash fires immediately after the shooting starts. Set to [Second-curtain synchronization] and use low shutter speeds for natural-looking shots of subject motion trails, such as car headlights. Set to [High-speed synchronization] for flash photography at higher shutter speeds than the maximum flash sync shutter speed. This is effective when shooting with an open aperture in < example. > mode to blur the background behind subjects outdoors in daylight, for Caution When using second-curtain synchronization, set the shutter speed to 1/60 sec. or slower. If the shutter speed is 1/80 sec. or faster, first-curtain synchronization will be applied automatically even if [Second-curtain synchronization] is set. Flash exposure compensation Just as exposure compensation is adjustable, you can also adjust flash output. Note If flash exposure compensation is set with the Speedlite, you cannot set the flash exposure compensation with the camera. If it is set with both the camera and Speedlite, the Speedlite's setting overrides the camera's. 165