ASA by purchio

We’re finishing up our basics of photography with ISO, or film speed. This builds on our previous episodes on the pinhole camera, shutter speed and aperture.

ISO applies to film, but it translates to the digital world. ISO stands for the International Organization of Standardization. The word order is French. The standard for color negative film is ISO 1500:1987, for black and white, it’s ISO 6:1983. You won’t see those listed on film canisters, but these are the standards document references. The ISO numbers that we are used to are the arithmetic scale. ISO is also available on a logarithmic scale, but it less common.

High speed films (higher numbers) allow more light, but also have the potential for more grain in analog photography or grain in digital photography. Lower speeds (lower numbers) are less sensitive to light. On the digital side of things, ISO refers to the sensitivity of the image sensor to light.