No abstract

A method of phase-contrast microscopy is described, not involving the use of special objectives or condensers. A method for making the phase-plate carrying a raised annulus is described. A large annular source of light is focused by the condenser of the microscope in a plane slightly below the object. The phase-plate is placed in the conjugate focus of this plane, just above the back lens of the objective.

With those low-power objectives in which a phase-plate can be placed near the back focal plane, phase-contrast microscopy can be obtained without the use of any condenser. The illuminating annulus is placed in the conjugate focus of the phaseplate.

A special electric bulb is described, with the filament in the form of an exact circle. It provides a very narrow annulus for phase-microscopy without any masking, and thus gives strong illumination without much heat. Increased contrast is obtained by the use of this method.