Dependence of Anomaloscope Matching on Viewing Distance or Field Size

Abstract

For the rapid detection of defective colour vision in personnel untrained in the use of optical instruments, an anomaloscope has been constructed in which a bipartite test field of 18 mm. diameter is viewed direct with both eyes. One half of the field is illuminated by light passing through a narrow-cut yellow filter (Ilford No. 812, maximum transmission at 580 mµ), and the other half by a variable mixture of the lights from a narrow-cut red filter (Ilfosrd No. 608, transmitting above 640 mµ) and a narrow-cut green filter (Ilford No. 807, maximum transmission at 530 mµ). The instrument was designed so that the proportions of red and green light in the mixed half of the field could be obtained with fair accuracy from the reading of a single scale, and a control was provided for adjusting the brightness of the other half of the field. The brightness of the field was about 10 candles per sq. metre, permitting observations to be made in artificial light or dim daylight.