When a person observes an object located at a distance closer than his near point, the object will appear blurred. Inserting a circular pinhole with a suitable diameter in front of the eye improves vision. However, vision worsens below a certain pinhole diameter, due to diffraction and increasing darkness. In this paper, the effect of the pinhole diameter on observation quality is investigated by determining the optical transfer function of the eye lens – pinhole system. A quantity that is a criterion for image quality is defined, then, it is calculated as a function of the pinhole diameter. This treatment shows that, even for a definite eye, the optimum and also minimum values of pinhole diameter depend on the object distance.
