Patent ID: 6783243
Filing Date: 2004-08-31
Classification: G03B

Abstract:
An overhead projector comprising:a transparent picture plate for supporting a transparent document having substantially opaque information provided thereon; a light source for illuminating the picture plate with a light beam; a projector head having an optical device and an oblique mirror to deflect the light beam illuminating the picture plate toward a projection screen so as to project the information provided on the document onto the screen; first and second polarizing layers positioned substantially perpendicular to the light beam and fitted at a distance from each other; wherein the first polarizing layer covers the picture plate and forms a supporting surface for the document, and the second polarizing layer is positioned in a path of the light beam close to the projector head; and wherein polarization directions of the first and second polarized layers are arranged to be perpendicular to each other, so that when no document is provided on the supporting surface the projection screen is not illuminated, whereas when the document is provided on the supporting surface transmission of light from parts of the picture plate located between edges of the document and edges of the picture plate is counteracted by the first and second polarizing layers and only the document is illuminated on the projection screen.