Interferometrie a double plage par photographie “speckle”

The image of a partial diffusor is recorded on a holographic plate. After development, the hologram is repositioned to observe “live fringes”. Half of the aperture of the optical system has been masked during the exposure, but the full aperture is used for the reconstruction. Two separate reconstructed images of the half aperture show two different interferograms. This set up can be used to measure displacements of objects, or defocusing.