The contrast threshold for perception of square-wave gratings as depending on spatial frequency is measured for varying viewing distances, adaptation and exposure time. The luminance varied between 1.4 and 110 cd/m<sup>2</sup>; target distances were 1, 3.1, and 7 m. Exposure times ranged from 1.5 msec to 1 sec and unlimited. A distinct minimum threshold contrast is observed for a definite spatial frequency, which depends on the viewing distance and luminance. A decrease in exposure time causes a less significant minimum. Exposure times from 40 to 1.5 msec do not alter the curve decisively. With exposure times less than 2 msec and spatial frequencies somewhat above 0.02 lines/min of arc the optical transfer function of the eye can be measured by determination of thresholds.
H. A. W. SCHOBER and R. HILZ, "Contrast Sensitivity of the Human Eye for Square-Wave Gratings," J. Opt. Soc. Am. 55, 1086-1090 (1965)