Sir Isaac Newton takes credit for the origin of the Inverse Square Law, which applies to physical law, such as light, sound, gravity and many other physical objects, including radio waves. In the case of photography, without citing mathematical equations, simply put, when a light source is moved twice the distance away from the subject, the light falling on the subject decreases four times. The light path also expands out over an area four times greater in width and height.
For example, image your light meter reads F/11 when your studio light source is five feet from your subject. If you move the light so that it is 10 feet from the subject, you will reduce the amount of light on the subject to ¼ of its previous power or two full F/stops. To properly expose your image you’d have to open the lens up to F/5.6 (allowing four times more light to enter the lens than when it was set at F/11). [Read more...]





