The invention concerns a method of and an apparatus for the measurement of the Amplitude Point Spread Function (APSF), of an Optical Imaging System (OIS), wherein the APSF is defined as the complex field distribution of the beam delivered by the OIS and originating from a point source. The apparatus comprising a) an illumination source b) a point object, PO1 irradiated by said illumination source c) an object beam coming from said point object, collected by the Optical imaging System and transmitted! to a Wavefront Sensing Device, WSD and, d) a computer with processing means adapted to acquire the data from said WSD and adapted to compute the Amplitude Point Spread Function and derived parameters associated with the OIS. In a generic embodiment, the WSD is realized by means of a Mach-Zehnder interferometer providing a digital hologram to the processing means. The invention may be advantageously used in the field of Digital Holographic Microscopy (DHM).