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aoresteen · Joined: 26 May 2004 Posts: 67 Location: Newnan, GA, USA

I'm trying to figure out how the film speed ratings of the 40's & 50's would relate to the current ISO ratings.

I think in the 40's Koday, Weston, and GE speeds were used:

200 Kodak = 40 Weston = 32 GE.

My question is what would Kodak 200 be equal to in the current ISO standards?

I also understand that around 1960 B&W film speeds were doubled to remove the 1 stop saftey factor that had been built in the ASA standards, which confuses the ratings further.

Thanks for your help.

Nick · Joined: 16 Oct 2002 Posts: 494

t.r.sanford · Posted: Fri Jun 11, 2004 3:04 am Post subject:

The "Focal Encyclopedia" has a table comparing older film speed scales to the then (c. 1969) prevalent British Standard/American Standards Association values. Weston 80 is (more or less) the same as ASA 100.

I had not been aware that Kodak had its own system, but then, I don't know when the ASA published its first standard. I seem to recall that the change in ASA sensitometric criteria took place a bit before 1960 -- I remember "Tri-X" being rerated from 200 to 400, but I don't remember just when; I'd guess 1958 or 1959.