Watkins & sons Exposure Meter Light meter

English, late 19th century, brass-made by R Field & Son, Birmingham, 6.8 cm high..

The Watkins Meter Company was a manufacturer of photographic light meters in Hereford, England. The company was founded after Alfred Watkins obtained a patent in 1890 on his light meter. The Standard Meter was initially made by R. Field & Co. of Birmingham; the Watkins Company took over production around 1900. The meter exposes a small portion of a strip of light-sensitive paper, which darkens during exposure. The time the light-sensitive paper needs to darken to the same shade as the surroundings of the slit is the third input parameter to calculate the correct exposure time for a given aperture and film speed, using the instrument’s calculation scales. The operation of the light-sensitive paper cannot be tested due to its age.