The present invention provides a method for on-axis visualization of a target placed in a photon beam, the method comprising: placing the target in the path of the photon beam; selecting a mirror with an external reflecting surface; placing the mirror on a mirror support so that the surface faces the target; placing a reflective microscope so as to collect photons emanating from the target that have been reflected by said surface; counting and analyzing photons collected by the microscope with a CCD camera; and storing and analyzing data collected by the camera.