Universal Stage

(also Fedorov stage), a special device attached to a polarizing microscope, enabling a thin section of a crystal to be held in various positions by rotating and tilting the section. The first model of a universal stage was proposed by E. S. Fedorov in 1891 and was based on the same principle as a theodolite, that is, on rotation about two horizontal axes at right angles. In 1896, Fedorov described a model with four axes; a fifth axis was added by the American scientist Emmons in 1929.

In the five-axis universal stage, the five axes are formed by three coupled theodolite systems and the axis of the microscope’s rotating stage. The universal stage is used to determine the optical isotropy, the optical axiality, the optical sign, the direction of the optical axes, the magnitude of the double refraction, and other optical properties of a crystal (seeCRYSTAL OPTICS).