Not only fish and snakes have scales

Toronto. An option to actinometers or extinction meters was the more sophisticated scales and nomographs. These devices like the Harrold Exposure Scale patented in 1922, or the JohnsonStandard Exposure” calculator, allowed a photographer to describe a scene and the lighting and then determine various combinations of speed and apertures needed to make a perfect exposure. Johnson was a British company that was known for its darkroom chemicals.

In the mid to late quarter of the last century each film contained a sheet of paper with a small table of the suggested exposures and a given speed and aperture combination. All films used a standard ASA (ISO) or DIN rating for film speed, making such simple papers of use for those without a sophisticated light meter.

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