Photography: What does ISO (ASA) mean ?

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In photography, what does ISO and ASA mean ??

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ISO stands for International Organization for Standardization

ASA is something American, and is unimportant.

In photography it is taken to mean the standard for measuring film speed, or how sensitive a film is to light. Obviously it is also now applied to digital camera sensors.

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  • Slap Happy answered 3 years ago
    Film speed standards.
    ASA = American Standards Association

    There were also separate British, German and Russian sets of standards.
    (British Standards Institute, Deutsches Institut fur Normung, and the GOST of Russia)

    ISO = International Standards association and they combined the American and German scales for the ISO standard numbers.

    The American scale ASA was based on a direct mathematical scale while the German system gave film speed on a logarithmic math scale.
    ISO gives both scales.
    You have the ASA style numbers from 6 to 102,400.
    You have DIN style numbers from 9° to 51°.

    Note that ASA numbers above 12,800 or 42°DIN are only on digital cameras because film is not able to give the same sensitivity.
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  • hellohello answered 3 years ago
    ASA is the old name for ISO.
    It depends if you're using film or digital photography. If it's film, then the ISO number is a rating telling you how sensitive the film is to light. The higher the number, the more sensitive it is, and the less time needed to expose a photo. So, it's best to choose a higher ISO for indoor or night photos, or wherever there is typically less light - however, high ISO films tend to produce a grainier effect on your photos.
    If you're using digital, then this is the camera simulating the effect of different ISO films.
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