Microscope illuminator usable both for bright field illumination and dark field illumination

Claim 1

A microscope illuminator usable for alternative dark field illumination and bright field illumination of an observation optical system comprising a light source; a shield plate disposed in the optical path between said light source and said optical system to prevent the light beams emerging from said light source from being directly incident along said optical path on the observation optical system of the microscope; a liquid crystal cell composed of two glass plates disposed in said optical path, provided on their opposing surfaces with a transparent electrode and enclosing liquid crystal therebetween and having a light transmitting state causing dark field illumination and a light diffusing state causing bright field illumination; an electrical switch and a power supply which is connected via said switch to said transparent electrodes of said liquid crystal cell so that the light conduction of said cell can be shifted from said transmitting to said diffusing state and vice versa by operation of said switch.