1932 · Selenium Photocell Exposure Meter · Work 809 of 1,871
A light meter of 1932 held up in a film studio in California, a hand in a dark suit sleeve holding an elongated oval case of glossy black Bakelite seventeen centimetres long and seven centimetres wide with a small metal eyelet at one end, its back turned toward the camera, its front with the small window and the photocells facing a brightly lit painted backdrop of a garden, behind the hand a large film camera in a padded cover on a wooden tripod, tall spotlights on stands, black cables across a wooden floor, a man in shirt sleeves seen from behind beside the camera, hard white light from the spotlights on the left.
What it was used for
The Weston Photronic 617 is a photographer's exposure meter with selenium photocells. Weston advertised the Photronic cell from October 1931. The Model 617/1 of 1932 was, per westonmeters.info, the first Weston instrument designed specifically for calculating camera exposure. It reads reflected light only. The photographer set the film speed - up to 48 on the Weston scale - on one dial and turned a concentric second dial until the pointer stood at the measured value; aperture and shutter speed were then read off the dial. The instrument has 2 cells and a push button that brings both into use; in that more sensitive setting the scale values were divided by 10.
What was new
The Photronic cell is a selenium barrier-layer cell that generates its own current - the instrument needs no battery; the 594-YY type delivers about 46 to 58 microamperes at 20 foot-candles into 200 ohms. Before it, exposure was judged with extinction meters, comparison photometers and actinometers that timed how long light-sensitive paper took to darken to a standard tint; the National Science and Media Museum calls Weston's 1932 design one of the first photoelectric meters, not the first. The barb: the twin-cell 617/1 was built for only about 2 years before the single-cell 617/2 replaced it.
What the sources leave open: No new price for the 617 could be verified, nor any production figures. Whether "Photronic" was a registered trademark is not stated outright by any page opened - prc68 shows the mark only in the title of a cited publication. The microampere values apply to the 594-YY cell type, not to the 617 meter.