| film speed |
The relative light sensitivity of the photographic emulsion (film). Expressed in ISO (International Standards Organisation) (ASA on older cameras), the film speed, or sensitivity to light, increases with the number. For example, an ISO 100 film requires less light than an ISO 50 film. Each time you double the film speed, half as much light is needed for a correct exposure. Faster films need less light but they produce grainier pictures. ...
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