Selenium meter

The inner (flat) circle rotates with the help of the knob and sets the film sensitivity (visible in both DIN and ASA units through tiny windows).

Various models of Zeiss Ikon Contaflex SLR and Contessa cameras have built-in coupled match needle selenium meters.

This kind of attempt to automate exposure setting was common in an era were precision mechanical engineers didn't know any limits of complication so that even further steps were gone to use selenium photo cells to control all exposure settings, or to control them more exactly with help of electro-mechanical aids.

It was a precision mechanical wonder that a handful of cameras were made which had automatic exposure control driven by a selenium meter, without need of further electronic or electromechanical support, for example the Optima.

The scale of these instruments show not an exposure value but an aperture value to be set "uncoupled" Examples of Leica and Tessina are shown in the photographs This article was originally based on "Selenium meter" in Camerapedia, retrieved on 4 August 2007 under the GNU Free Documentation License.