ABSTRACT
In any imaging application it is important to know how well the energy is concentrated around the geometrical image point; the better this concentration, the better the imaging. An efficient computational technique is to use partly ray tracing and partly diffraction theory. In this combined method, ray tracing is applied to determine how the wave propagates all the way from object space through the optical system and up to some reference plane in image space. Thereby one finds how the real wave emerging from the system deviates from a converging spherical wave centered at the Gaussian image point, or, phrased differently, one finds the amplitude and phase of the emerging wave in the reference plane. In the majority of situations encountered in optical imaging, the last vertex plane of the system may serve as reference plane. Traditionally lens designers have used only ray tracing, despite the fact that it breaks down in the vicinity of the image point.
