Figure 10.  The shift in interference patterns for a single slit of an appropriate width as a function

of distance from the screen. As the screen is moved closer to the slit, the Fraunhofer pattern (a) observed far from the slit gradually changes into the Fresnel pattern (d) observed near the slit.  For a circular aperture the Airy diffraction pattern of Fig. 7-E would be obtained at large distances.  Presented in (A*) is an expanded presentation of the conditions of (a) that include Zones A and B of Fig. 9.   Locations of minima and maxima outside the central diffraction maximum may be calculated utilizing Huygens principle as illustrated in Fig. 12, or when based on the pulson model, the format for the double-slit arrangement may be utilized with each edge acting as a slit.