| Abstract: | A phase-contrast device comprising objectives provided with two concentric phase rings, one positive and one negative, and a condenser with aperture diaphragm provided with two concentric transparent rings conjugate with the phase rings and covered by two crossed polarizing films, is described. The change of image contrast from positive to negative, and vice versa, is obtained by rotation of a polarizer placed before the condenser or above the objective. Properties and advantages of the device are discussed. |
