The Depth of Field of the Human Eye

A simple but accurate method of measuring the depth of focus of the human eye is described. 2. At a fixed pupil size the hyperfocal distance was found to increase directly with the log of the background luminance over the photopic range. 3. If the luminance and pupil size is held constant the hyper-focal distance is found to vary linearly with the contrast. 4. If the contrast and the retinal illumination is held constant, the depth of field varies approximately inversely with pupil size. 5. With pupil diameters greater than 2.5 mm the observed deviation of the hyperfocal distance from theoretical expectation can be accounted for by the operation of the retinal direction effect of Stiles and Crawford. 6. Further evidence that the retinal direction effect modifies depth of field has been obtained by measurement with fields of different colour but similar luminance. 7. Correction of the chromatic aberration in the eye by means of an achromatizing lens decreases depth of field. The reason for this appears to be the reducion of the coloured fringes around a retinal. image rather than the decrease of the chromatic difference of focus produced by the achromatizing lens. 8. The minimum estimate for depth of field obtained in these experiments under optimum conditions of contrast and luminance was about +- 0.3 D at a pupil diameter of 3 mm. 9. The results obtained by other workers in this field are discussed in the light of the present results.