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 Johnson “Standard 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.