GB678330A - A device for observing transparent objects - Google Patents

Abstract

678,330. Phase contrast devices. CENTRE NATIONAL DE LA RECHERCHE SCIENTIFIQUE. June 23, 1950 [June 24, 1949; Feb. 3, 1950], No. 15791/50. Class 97 (i). A phase contrast device for observing transparent objects comprises a transparent hemisphere divided into two parts 1, 2 by a plane parallel to the base of the hemisphere and at a distance therefrom equal to half the radius. The surface of separation of the parts 1, 2 is semi-reflecting and located between the parts and centred on the axis passing through the centre and top of the hemisphere is a phase plate. Part 2 of the hemisphere is coated with reflecting material, except for a portion 5 located at the top thereof. In the form shown, the phase plate Q is annular and, in use, an image is formed thereon of an annular diaphragm D by a condenser E, E<SP>1</SP>. A rotatable polarizer R and a conical half-wave plate C are included in the illuminating unit and the internal diameter and radial thickness of the phase plate Q are such that a ray issuing from a transparent object O and reaching a point half-way between the inner and outer peripheries of the phase plate is incident on the latter substantially at Brewster's angle. An image of the object O is formed at O<SP>1</SP> in phase contrast and, by rotating polarizer R, the contrast can be varied. Another form is described wherein the phase plate comprises a transparent annulus surrounding an opaque area.