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 <nowiki>"ASA number" or the "film speed"</nowiki>. 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.