Unexpected automation

John Wade examines the ingenious ways mechanical cameras tackled automatic exposure

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At the heart of a camera's automatic exposure system lie three basic procedures. First came shutter priority, in which the photographer chose a shutter speed and the camera automatically set the correct aperture. Then came the more popular aperture priority, allowing the photographer to select an aperture, leaving it to the camera to set the correct shutter speed. Finally, both shutter speeds and apertures were chosen automatically and set with a program mode. All of which took off big time when battery-driven electronics hit cameras in the 1970s. What you might not know is that automatic exposure modes like these go back much further, to the days when meters were activated by selenium cells that didn't need batteries to operate, and when automation relied on mechanical levers, rotating cogs, expanding and contracting springs and even compressed air. Welcome to the world of mechanical auto exposure, whose cameras are today both collectable and usable.

1938: Super Kodak Six-20

The first camera to incorporate an electronic exposure meter was the Zeiss Ikon Contaflex in 1935. But that meter only recommended correct apertures against shutter speeds that then needed to be set manually. The first camera to use a builtin exposure meter to actually activate an automatic exposure system was the Super Kodak Six-20.