I typically adjust the flash exposure compensation down a stop or two when using fill flash outdoors, so I'm familiar with the effect it has on exposure, but how does the camera adjust exposure when this value is set?

In my limited understanding, the following parameters will affect exposure:
  • Shutter speed
  • Aperture value
  • Metering method
  • ISO speed


It seems these values are not modified in a flash exposure compensation mode.
So exactly what does the camera do in this situation?
Is it just adjusting the final brightness value or is something more complex going on?