Dependence of Anomaloscope Matching on Viewing-Distance or Field-Size

Abstract

IN a recent communication bearing the above title¹, we pointed out that with a particular anomaloscope the R/G ratio in the mixture required to match a narrow-band yellow depended on the viewing distance. Further work on more than forty normal observers has confirmed this effect, and also established the fact that the effect for each observer is substantially the same whether one eye is used or two eyes, as in the original investigation. Most observers required more green in the mixture the greater the viewing distance. Taking the R/G ratio a unity for an observer viewing an 18-mm. field at 60 cm. (subtending 2°), the ratio drops at a decreasing rate to an average value of about 0·85 at 300 cm. (20 ft.), beyond which there is little further change. The spread of results for different individuals is considerable, some observers dropping below 0·6.