Photographic film
Examples of ISO numbers are ISO 50, ISO 100, IS0 200, ISO 400, ISO 800, and ISO 1600. The ISO number is sometimes called the ''ASA number'' or the ''film speed''. When the ISO number is low, for example ISO 50, the film takes a long time to record the picture. This is called a slow film. This means the shutter has to stay open for a long time. When the ISO number is high, for example ISO 800, the picture is made in a very short time. This is a fast film. This means the shutter has to open and close quickly.