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Thread: speed rating ASA/ISO

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    Ausphotography Regular Boo53's Avatar
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    speed rating ASA/ISO

    I've been cleaning out some old stuff which has been stored in the roof for ages and came across an old flash gun which is about 35 years old.

    It was a pretty good bit of gear in its day with several settings and rated out to 40'.

    Some of the dials are set out in ASA ratings.

    Is that equivalent to ISO, or is there a difference?

    John R

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    Administrator ricktas's Avatar
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    ASA and ISO are the same thing

    ASA used to be used in some parts of the world, there was also a littler known European standard called DIN. They all mean the same thing, and ISO became the world standard. An ASA 100 film is the same as an ISO 100 film.

    The ISO/ASA represented the 'speed' of the film based on its level of sensitivity to light. An ISO 200 film is twice as sensitive to light as an ISO 100 film, and a 400 is twice as sensitive as a 200.

    The digital equivalent has been to use the same system of ISO to determine how sensitive the camera sensor is to light, but the overall idea behind ISO remains the same, for film or sensor.
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    Member NikonUser's Avatar
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    The current ISO for digital sensitivity corresponds to the ASA system I'm pretty sure.

    Usually wouldn't use wikipedia as a reference... but a quick google found this:

    http://en.wikipedia.org/wiki/Film_sp...ent_ISO_system

    Paul

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    It's all about the Light!
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    FYI In the stickies in this forum... http://www.ausphotography.net.au/for...hread.php?t=30 (Dictionary)
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    Thanks Rick, Paul & Kym.

    I assumed they were equivalent but if I hadn't checked Murphy's Law would have meant I was wrong.

    Kym. I did have a fair bit of a search around the site before posting but I must admit I never thought of looking in the Dictionary - thanks for that

    John R

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    For those who aren't aquanted with Standards, the Letters ASA, ISO & DIN are actually acronyms for Standards organisations around the globe, like here in Australia with Australian Standards (AS).

    ASA - American Standards Association

    ISO - International Organization for Standardization

    DIN - Deutsches Institut fur Normung - the German Institute for Standardization

    Its actually very fortunate that all three standards are actually the same ie 100 ASA = 100 ISO = 100 DIN. The large majority or standards in the world all manage to come up with some reason that they need to be different due to local demand. Imagine getting film or camera setting where 100 ISO operates on a different number if read in the ASA setting or even worse a different logrithmic numerics scale ie 2 = 5 but 3 = 27 and 4 = 103 - almost impossible to calculate without knowing the base algorithm.

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    Arch-Σigmoid Ausphotography Regular ameerat42's Avatar
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    Quote Originally Posted by MarkW View Post
    Its actually very fortunate that all three standards are actually the same ie 100 ASA = 100 ISO = 100 DIN.
    Wrong, actually. DIN is not at all on the same scale as ISO and ASA, for example, ISO/ASA100 is equivalent to DIN 21 (with a little symbol for degree). If I recall, three DIN steps were equivalent to a doubling of ISO/ASA, so that ISO 400 would be equivalent to DIN 24.
    Am.

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    Quote Originally Posted by ameerat42 View Post
    Wrong, actually. DIN is not at all on the same scale as ISO and ASA, for example, ISO/ASA100 is equivalent to DIN 21 (with a little symbol for degree). If I recall, three DIN steps were equivalent to a doubling of ISO/ASA, so that ISO 400 would be equivalent to DIN 24.
    Am.
    Correct! http://en.wikipedia.org/wiki/Film_speed
    DIN is a logarithmic scale and ASA/ISO is arithmetic

    As people have enough trouble with f/stops (square roots as it's about area), imagine adding in a log scale

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    Arch-Σigmoid Ausphotography Regular ameerat42's Avatar
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    Thanks, Kym. I was a bit out above. I should have said that ISO 200 is equiv. to DIN 24.

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    It's all about the Light!
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    Quote Originally Posted by ameerat42 View Post
    Thanks, Kym. I was a bit out above. I should have said that ISO 200 is equiv. to DIN 24.
    No drama. The link shows the ISO/DIN conversion.
    DIN is not used nowadays (or ISO is published as well).
    It's only any use for very old film stock per OP, which is probably useless anyway.

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    Quote Originally Posted by ameerat42 View Post
    Wrong, actually. DIN is not at all on the same scale as ISO and ASA, for example, ISO/ASA100 is equivalent to DIN 21 (with a little symbol for degree). If I recall, three DIN steps were equivalent to a doubling of ISO/ASA, so that ISO 400 would be equivalent to DIN 24.
    Am.
    Oops, I must have miss read the article, I thought that DIN went up the same as ASA, I should have known it was too good to be true.

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