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Thread: What does ISO mean >?

  1. #1
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    Question What does ISO mean >?

    yeah as above


    i know in dark .....better to use higher ISOs and stuff ......

    but what does it really mean ?

  2. #2
    ajacent
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    Hmmm thought it was commonly known as asa speed, no?

  3. #3
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    ISO just stands for the International Standards Organisation. Basically it's just a set standard that the manufacturers agree to adhere to so that the consumer has a reasonable assurance that an ISO of 100 from any manufacturer is going to yield a reasonably similar film speed.

    ASA was the old standard, set by the American Standards Agency. Essentially the figures used were exactly the same. However the old Eastern European countries used the DIN measuring scale, which require a different reference point altogether. In the hope of standardising things, the ISO standard was adopted instead.

    A bit like metric and imperial really.

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    film speed ?
    what does that mean ??

  5. #5
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    Originally posted by BlueAngel
    film speed ?
    what does that mean ??
    In general parlence the term 'speed' indicates how a film behaves when exposed to light under a given set of conditions. The 'faster' a film the less amount of illumination is required to produce an acceptable image while slower films require more illumination.

    This is a really simple version of what film speed actually is.


    NOTE:
    The exact requirements for classifying a film and giving it an ISO or other rating number is very complicated and well beyond the scope of this reply as it would require quite a few pages to explain the core concepts yet alone the actual proceedure.
    Last edited by Ian; 17th November 2002 at 08:55 PM.
    The Ang Moh from Hell
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    i see
    thnkx

  7. #7
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    doh! I should have mentioned that the smaller the ISO number the slower the film.

    The standard ratings for film runs like this:

    25, 50, 100, 200, 400, 800, 1600, 3200

    Each of those 'speeds' or ratings represents a 1 stop difference in speed. In otherwords doubling or halving of the exposure time depending on which way you go up or down the scale.

    Thus 100 is twice as fast as 50 and half the 'speed' of 200 and so on.

    There are other film speeds as well such as ISO 64, 125, 160, 320 etc.
    The Ang Moh from Hell
    Professional Photography - many are called, few are chosen!

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