How to Convert Film Speed From Scheiner to ISO
The speed of camera film is a measure of the light required to expose the film and create an image. During the film camera era, film manufacturers, light meter manufacturers and photographers used a variety of standards to express film's speed. The first system was set out by German astrophysicist Julius Scheiner in 1894. As film speeds increased over the ensuing decades, his system was replaced by the DIN system and the current ISO system. Some vintage cameras and light meters use the Scheiner system, so it's useful to know how to convert between Scheiner and modern ISO ratings.
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Instructions
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Locate a film speed conversion table in a photography textbook, or use an online conversion table (see Resources).
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Look up the Scheiner rating of the film your camera manual or lightmeter reading specifies. You need to know whether your equipment is American or European because there were different versions of the Scheiner scale in use.
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Follow the cross-reference across the chart to the corresponding ISO or ASA number for the film. For example, common ISO 100 film corresponds to 28 degrees on the American Scheiner scale and 34 on the European Scheiner.
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Tips & Warnings
There were significant differences between brands of equipment and film in the early years of photography. Any conversion between Scheiner and more modern film speed standards is approximate at best. In practice, you will usually need to experiment with your camera's settings to accommodate the specific brand and speed of film you use.
References
Resources
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