The Inverse square Jaw The Inverse square Jaw is the basis for flash exposure calculations.  The farther the light travels, the more the light rays spread out and the dimmer the  resulting illumination. …see full text To Calculate your own Flash Exposure To calculate your own flash exposure you need to know two things: the distance that the light travels to the subject and the guide number (a rating given by the manufacturer for the flash when used with a  specific film speed) …see full text Bounce Flash Travels an Extra Distance If you are calculating a bounce flash exposure, measure the distance not from flash to subject but Read more