Legge G E, Mullen K T, Woo G C, Campbell F W
J Opt Soc Am A. 1987 May;4(5):851-63. doi: 10.1364/josaa.4.000851.
Low-resolution optical systems are more tolerant to defocus than are high-resolution systems. We wished to determine whether this principle applies to human vision. We used psychophysical methods to measure the effects of defocus in normal eyes under low-resolution conditions. Modulation transfer of sine-wave gratings was measured as a function of dioptric defocus at low and medium spatial frequencies. We defined the depth of focus at a given spatial frequency to be the dioptric range for which the modulation transfer exceeds 50% of its peak value. For dilated pupils, depth of focus increased from about 2.5 diopters (D) at 3.5 cycles/deg to about 17 D at 0.25 cycles/deg. From our results we predicted that tasks requiring only low spatial frequencies will be more tolerant to defocus than tasks requiring higher spatial frequencies. This prediction was confirmed in a letter-recognition experiment. The increasing tolerance to defocus at low spatial frequencies also implies that individuals with low acuity will be more tolerant to defocus than people with normal vision. We confirmed this prediction by measuring tolerance to defocus in 30 low-vision eyes.
低分辨率光学系统比高分辨率系统对散焦更具耐受性。我们希望确定这一原理是否适用于人类视觉。我们使用心理物理学方法来测量在低分辨率条件下正常眼睛中散焦的影响。测量了正弦波光栅在低空间频率和中空间频率下的调制传递函数随屈光度散焦的变化。我们将给定空间频率下的焦深定义为调制传递超过其峰值50%的屈光度范围。对于散瞳，焦深从3.5周/度时的约2.5屈光度（D）增加到0.25周/度时的约17 D。根据我们的结果，我们预测，仅需要低空间频率的任务比需要更高空间频率的任务对散焦更具耐受性。这一预测在字母识别实验中得到了证实。在低空间频率下对散焦耐受性的增加也意味着低视力个体比正常视力的人对散焦更具耐受性。我们通过测量30只低视力眼睛对散焦的耐受性证实了这一预测。
