Testing of great aperture objectives by means of phase modulation interferometry

The differential interferometry which is able to obtain the self comparison of the wavefront for a given spatial frequency offers solutions proposed by several authors. The authors have considered the use of a polarization interferometer associated with a phase modulation to increase accuracy. In spite of some non-negligible experimental complications, it is effectively possible to obtain directly the components of the MTF. In so far as a limited number of informations about some discrete frequencies are interesting the user such an instrumental project could be considered.