Historylinks Year: 1960
A Johnson Standard Exposure Calculator c 1960 sold as a aid to photographers, prior to the advent of automatic cameras, to calculate an exposure value, indicating the relevant shutter speeds over a the range of aperture settings f2.8 to f22. The instructions, printed on the device, outline the simple process to determine camera settings: "Rotate disc until the arrow marked 'Start' points to the arrow marked 'No Filter' or, when a filter is in use, to the appropriate filter factor. Dial the 'Subject' on this side of calculator. Then turn over and dial 'Light Value', 'Film Speed' and 'Weather' on the back, always dial clockwise finishing at the 'Stop'."
Picture added on 15 May 2019 at 11:29