Originally Posted by
inkista
Ambient is controlled by iso, aperture, and shutter speed.
Flash is controlled by iso, aperture, flash power output, and flash-to-subject distance.
So, the idea that aperture influences flash output is partly incorrect; like ISO, aperture also controls both flash and ambient together. Shutter speed is the only independent setting in the triangle, because if the camera is at or below sync speed, then the flash burst is going to be much much faster than the shutter speed, so leaving the shutter open for longer won't gather any more light from the flash.