Figure A2-3. Phenomenon of Diffract

Figure A2-3. Phenomenon of Diffraction of Light on the Pupil.b. The operation of the eye as an optical apparatus is also harmed to a certain degree by the lightdiffusion occurring with in it. It is especially discernible when one views brightly illuminatedobjects located against a dark background. The effect of light diffusion in the form of a more orless noticeable radiation, covering the field of vision, is caused by media which do not possessabsolute transparency -- the crystalline lens and the vitreous humor. The light diffusion in theoptical media is responsible for the halos of light. They are especially noticeable where thetargets are strongly illuminated by sunlight. In such an instance, the white background of thetarget casts a sharp reflection and causes a considerable light diffusion in the optical media. Thiscauses a blinding effect. Both the bull's-eye, perceived by the eye in the form of a gray spot withindistinct edges, and the front and rear sights are perceived with unclear outlines.c. It is obvious from what has been said that the amount of light diffusion from spherical aberrationis in direct proportion to the size of the opening of the pupil, and the amount of light diffusion fromdiffraction is in inverse proportion to the size of the opening of the pupil, and thus it is not possibleto eliminate these types of diffusion completely. As a result of this inverse dependence of theeffects of aberration and diffraction upon the size of the pupil, the best conditions of sharp visioncorrespond to a certain average size of the pupillary opening -- a diameter of approximately 3mm