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Equivalent exposure rating. Advice needed.

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    Paulbee e2 Member 1035 forum postsPaulbee vcard United Kingdom
    6 Dec 2006 - 4:18 PM

    Is the old ASA rating the same value as ISO, or do I need to multiply the ASA rating by a correction factor?
    I have recently had reason to doubt the exposure readings given on my Canon 300d,(badly over exposed), so I decided to dig out my old, and little used, WestonMaster III to give a comparison. As I hav'nt used it for about fifteen years it jolted the memory a bit to see the speed rating given as "Weston Rating". I think I remember that we treated this the same as ASA at the time, but what equivalent to ISO is ASA ? Any info on this would be a help,
    scanned the forum topics but couldnt find anything.
    Thanks, Paul.

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    Nike55  8956 forum posts United Kingdom
    6 Dec 2006 - 4:26 PM

    ASA is American Standards Association
    ISO is International Standards Organization

    When most film was made in the USA the ASA determined the standard for film speed.

    In parts of Europe the standard was ISO (International Standards Organization)

    ISO is the same as the ASA standard but now adopted by all.

    I still use the term ASA when winding up people on here Wink


    Helpful Post! This post was flagged as helpful
    Paulbee e2 Member 1035 forum postsPaulbee vcard United Kingdom
    6 Dec 2006 - 5:27 PM

    Thanks for that, now I know its the same.

    PS I don't use a winder these days, the new camera has battery.

    6 Dec 2006 - 5:51 PM

    film speed scales

    Helpful Post! This post was flagged as helpful
    c_evans99  107013 forum posts Wales1 Constructive Critique Points
    6 Dec 2006 - 6:39 PM

    Weston Ratings didn't always strictly match the ASA scale of the day and the company used to issue pamphlets of Weston Ratings periodically. I think they switched to ASA around the time the Master IV came out.


    6 Dec 2006 - 6:44 PM

    Quote: ......the company used to issue pamphlets of Weston Ratings.....

    I have one somewhere

    Paulbee e2 Member 1035 forum postsPaulbee vcard United Kingdom
    7 Dec 2006 - 2:22 PM

    Thank you everyone for your input, Your info Barry takes some time to absorb. I will have to download it and read it again.
    I suppose ISO has simplified the situation which existed where films were rated in both ASA (American Standard Association) and DIN (Deutsche Industrie Nummer) at the same time.
    Regards everyone, Paul.

    devo  7
    23 Jan 2007 - 6:07 PM

    Try this---i have used old westons for years!,up until the introduction of -"the weston master "5", it was the "old-type ratings.I use a "3".a "5", and a"euromaster".there is 20-30 years between these meters, and they are all still spot on,every time with incident readings.---Anyway,here is a simple conversion table,to keep in your gadget bag!---ASA--25=WESTON--20,--ASA--50=WESTON--40--ASA--100=WESTON--80--ASA--125=WESTON--100,ASA--400=WESTON--320,ASA--1000=WESTON--800.--hope you find this helpful!.

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