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The classic example was the light globe used in a polaroid camera. The globe was powered from a mercury cell, and because it's voltage was so constant, the lig
by Johnythree 9y ago
The classic example was the light globe used in a polaroid camera.
The globe was powered from a mercury cell, and because it's voltage was so constant, the light stayed at constant brightness.
Then a simple plastic lens overlayed alternate stripes from the image and the globe. The user adjusted the aperture until the stripes vanished, which guaranteed that the exposure was correct.