Computed transfer functions for ε=0.60 and 0.75 annular pupils of 2.67 mm o.d. showthat absorption of the average spherical aberration of the eye is still incomplete but if theeye is so designed as to adjust its focal plane in order to achieve a best Strehl ratio, itwould show a transfer function approaching that of a diffraction limited system, i.e. the opticaldefect of the eye is overcompensated. However, it is argued that a varying amount offocusing adjustment of the eye is needed in order to account for the transfer function ofthe eye of different pupil sizes, though not always to the extent of achieving a best Strehlratio. Such a property of the eye is referred to variously as the antidefocusing, deblurringor contrast constancy phenomenon and, when operationally defined, this is equivalent to sayingthat the eye has a greater depth of focus than that defined for a physical system based upona fixed demodulation criterion. The signifi ance of the physiological depth of the eye isdiscussed. Computed transfer functions for ε = 0.60 and 0.75 annular pupils of 2.67 mm od showthat absorption of the average spherical aberration of the eye is still incomplete but if theeye is so designed as to adjust its focal plane in order to achieve a best Strehl ratio, itwould show a transfer function approaching that of a diffraction limited system, ie the opticaldefect of the eye is overcompensated. However, it is argued that a varying amount of focus of adjustment of the eye is needed in order to account for the transfer function of the eye of different pupil Such a property of the eye is referred to variously as the antidefocusing, deblurringor contrast constancy phenomenon and, when operationally defined, this is equivalent to saying that the eye has a greater depth of focus than that defined for a physical system based upona fixed demodulation criterion. The signifi ance of the physiological depth of the eye isdis cussed