In film photography, a measure of a film’s “speed” or light sensitivity. The higher the ISO, the more sensitive the film. The sensitivity of digital camera sensors are also rated using the ISO scale. ISO stands for the International Organization for Standardization (or, International Standards Organization, if you want an acronym that fits better) the people who define, among many other things, the spec used to gauge light sensitivity. ISO is equivalent to the old ASA scale (American Standards Association) which has since been discontinued. (Curiously, ISO is not meant to be an acronym for anything, it’s allegedly a pun on the Greek prefix “iso-” meaning “same.”)
ISO is one of three exposure controls that you have on a digital camera, in addition to aperture and shutter speed selection. Each exposure control allows you to affect different image characteristics.
||You can learn about each of these controls, how to use them, and how they affect your final image in Chapter 7 of Complete Digital Photography, 3rd edition.|