For correct flash exposure, 4 things need to be controlled and balanced:
- distance (from the flash to subject)
- power (the flash's actual blitz of light, taking into consideration any diffusion)
Two things relate to camera settings, and two things relate to the flash itself.
To really understand flash photography, it is essential to memorize those 4 things.
If you need an acronym to remember things more easily: PAID
Power, Aperture, ISO, Distance.
There are distinct ways in which flash exposure is controlled though - Manual Read more inside...