An f-stop is a designation to indicate a camera’s aperture opening, and a flash unit’s power level. Our flash units are measured in power over a range of available f-stops, indicating the high or low power level setting of the unit. Each f-stop (shown on the back panel of our flash units) lets in twice as much light as the f-stop before it, and half as much light as the f-stop after it. Over a 5 f-stop range, the power is adjustable from Full down to 1/32 of the total power. For f-stops in relation to your camera’s lens opening, see aperture.