DX coding is a system of markings on a film cassette that can be read by sensors inside a camera's film chamber. These codes convey important information about the film, including its ISO speed, exposure type, and the total number of exposures available.
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DX coding allows compatible cameras to automatically set the correct exposure settings, improving convenience and reducing the risk of incorrect exposure. This feature was widely used in 35mm film cameras, helping photographers achieve consistent results without manually adjusting the camera for each roll of film.