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 from flash to reflecting surface to subject. …see full text

PDF: How to Calculate your own Flash Exposure