- The ISO film speed standards help photographers choose the correct film -- or in the case of digital photography, the right settings -- to achieve a clear image. The current ISO system, issued in 1987, is a combination of the American Standards Association (ASA) and Deutsche Institut fur Normung (DIN) systems of film classification. Some manufacturers make films in a wide range of speeds while photographers choose some brands because they specialize in lower or higher film speeds.
- The film ISO number tells about the film's sensitivity to light. Photographers use ISO 100 film for what is called "normal" light conditions. However, if it is darker, a faster film speed is needed to get the same quality of exposure and detail. For example, an ISO 200 film needs only half the amount of available light in comparison with the 100 film and allows the photographer to use a faster shutter speed.
- Photographers talk about the "graininess" of an image. This effect results from film speed. For example, fast film -- ISO 400 and above -- produces grainier images than slow film. This is due to the fact that the film has more grains in its composition, and these stick together to form spots visible to the naked eye, particularly if you enlarge the image. In digital photography, which uses pixels, graininess is called "noise." Programs such as Photoshop have noise reduction features for digital photographers.
- Although a digital camera doesn't use film, it has a mechanism that simulates ISO film speeds. These are frequently found in the manual settings but are not available when you use a digital camera in auto mode. Professional photographer Geoff Lawrence suggests using ISO 200 setting for most photographs and changing the setting to the ISO 1600 maximum for night or indoor shots where there is very little light.
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