# What is ASA? Film Guys



## Darton (Feb 2, 2010)

I've got an old Gossen light meter with a couple attachments. Whilr reading the origional instruction manual for the meter it says to set the dial to the correct ASA for the film you are using. Ok i'm shooting digital. So what is ASA? Is it likr ISO or the same thing?


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## Big Mike (Feb 2, 2010)

> Is it likr ISO or the same thing?


Same thing.

ASA = American Standards Association
ISO = International Standards Organization


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## Battou (Feb 2, 2010)

Big Mike said:


> > Is it likr ISO or the same thing?
> 
> 
> Same thing.
> ...



^^^

+1


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## Darton (Feb 2, 2010)

Battou said:


> Big Mike said:
> 
> 
> > > Is it likr ISO or the same thing?
> ...


 
Sweet Thanks!!


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## Dwig (Feb 2, 2010)

Big Mike said:


> > Is it likr ISO or the same thing?
> 
> 
> Same thing.
> ...



When it comes to film speed, you can consider them interchangeable. When it comes to the detailed science behind the ratings, there are differences. 

There were two versions of "ASA". The original standard was labled "A.S.A." and the standard was maintained by the American Standards Institute. 

A later standard changed the testing method somewhat, becoming more similar to the German DIN systems' testing, and the label changed to omit the periods, "ASA". At that time the old American Standards Institute had been restructured as the American National Standards Institute (ANSI). They chose to use "ASA" instead of "A.N.S.I" or "ANSI" to avoid unnecessary confusion, although all of the other standards they published were listed as ANSI standards.

The modern ISO is an international standard and the testing specs are very slightly different. Originally, ISO could be listed using "ASA" units or "DIN" units, though the latter are really obsolete at this point and only the "ASA" units are used.


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