The zone plate radii given by Eq. (13-20) were derived for the case of plane waves inciden...

The zone plate radii given by Eq. (13-20) were derived for the case of plane waves incident on the aperture. If instead the incident waves are spherical, from an axial point source at distance p from the aperture, show that the necessary modification yields

where q is the distance from aperture to the axial point of detection and L is defined by 1/L = 1/p + 1/q.

Figure 1.