Actinometers for Photography (British Patent No. 4624, 1886)

Actinometers for Photography (British Patent No. 4624, 1886)

Author: William Ford Stanley and William Low Sarjeant

Year: 1886

Summary British Patent No. 4624 (1886), granted to William Ford Stanley and William Low Sarjeant, describes a compact photographic actinometer designed to provide photographers with a simple and portable means of estimating exposure. The invention was intended to be small enough to be carried on a watch chain while retaining the essential features required for measuring the actinic intensity of daylight. The patented actinometer consisted of a circular metal case resembling a small pocket compass. Within the case was a roll of sensitized paper wound around a central spindle, one end of which could be drawn through a narrow slot into a glazed exposure chamber mounted on the edge of the instrument. During use, the sensitized paper was exposed beneath the glass and compared visually with a permanently tinted standard attached to the underside of the glazing. When the exposed paper darkened to match the standard tint, the elapsed time provided a measure of the actinic strength of the light and could be used to determine the appropriate photographic exposure. A notable feature of the invention was the substitution of bromine-sensitive paper for the silver-chloride papers commonly employ