DOOR INSPECTION HOLE Russian patent published in 1997 - IPC

FIELD: optical systems of door inspection holes making it possible to observe persons or objects positioned on the outside within limits of vision field. SUBSTANCE: door inspection hole includes inverting prism unit composed of two rectangular prisms matched with reflecting faces and of three positive lenses installed in series and forming erect real image on screen which is flat lusterless surface of third collective lens facing viewer. Biconvex intermediate and plano-convex collective lenses have equal curvature radii of surfaces. EFFECT: enhanced efficiency and safety of door inspection hole. 5 cl, 2 dwg