The paper presents the mathematical technique for precise calculation of the three dimensional point spread
function (3D PSF) of a high aperture optical system. The proposed technique is based on Huygens-Fresnel principle: a
spherical wave at an exit pupil is considered as a numerous set of elementary secondary light sources. They emit
spherical coherent electro-magnetic waves. All these waves form a definite distribution of summarized complex
amplitudes in a three dimensional space near a focal point. This distribution is used for calculation of the distribution of
effective intensity which takes into account the influence of inclined optical beams. The comparison analysis of this
approach and the techniques based on multi-dimensional Fourier transforms are discussed.