In the diagram, the dotted line travels through the center of the lens and thus does not diffract. The ray r at the top of the aperture defines a certain path. If the angle q is chosen such that the marked distance equals one-half wavelength, then the dotted ray and the marked ray are 180¬° out of phase and their regions of overlap appear dark. Repeating this procedure at the next q such that r is canceled by another ray in the manner of the first case yields a second point of minimum intensity. Midway between these points of minimum intensity are points where the rays are fully in phase. At these points, the maximum intensity of the light is displayed. In general, if a is the height of the aperture, then the positions of maxima and minima, respectively, are given by
