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Equivalent exposure rating. Advice needed.

Paulbee 13 41 United Kingdom
6 Dec 2006 4:18PM
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 12 957 United Kingdom
6 Dec 2006 4:26PM
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

Paulbee 13 41 United Kingdom
6 Dec 2006 5:27PM
Thanks for that, now I know its the same.

PS I don't use a winder these days, the new camera has battery.
randomrubble 13 3.0k 12 United Kingdom
6 Dec 2006 5:51PM
c_evans99 14 7.0k 1 Wales
6 Dec 2006 6:39PM
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.

User_Removed 12 4.9k England
6 Dec 2006 6:44PM

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

I have one somewhere
Paulbee 13 41 United Kingdom
7 Dec 2006 2:22PM
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 11 14
23 Jan 2007 6:07PM
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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