This method its use to expand the contrast in transparent/non colored specimens witch permit to see some invisible features and gain some information about the optic density of it. With this technic it is possible to achieve images in black and white on a grey background. The main difference between this type of method and the phase contrast is bright diffraction aureole. The polarize light passes for two birefringent primes and then it will be divided in two different directions having as a result one image in 3D that represents the variations of the optic density.