Quote:
Originally Posted by Michael
A and C represent respectively the lower and upper limits of colour film range. "After setting the dial for any scene, all objects whose light values fall on or between these two positions will be correctly exposed". U and O are as you thought, I presume for monochrome film.
I quote from Instruction book: Weston Master II model 735 universal exposure meter, no explicit date but I think about 1949.
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It's fascinating to note that before this Weston Master II (1945) manual was published, the manuals for the Weston Model 617 Type 2 meter (1934) and the Weston Model 650 (1935) don't mention colour film - because it wasn't used in photography until the 1940s - and so the meaning of "A" and "C" don't relate to colour photography in those early manuals. Instead, "A" and "C" are simply used to signify minor shifts from the "B" (Normal or arrow) setting to compensate for a lack of contrast or an excess of contrast respectively. It seems like only later did Weston start to use "A" and "C" to cover the range of colour film.
As a final observation, in the Weston Model 617 Type 2 manual then "A" is 1.33 stops down from "B" (Normal or arrow) and "C" is 1.66 stops up from "B". However, in the Weston Model 650 manual then "A" is 1 stop down from "Arrow" (B becomes an arrow in this manual) and "C" is 1 stop up from "Arrow". This is how it stays for the rest of Weston's history.