| 摘要 |
PURPOSE:To provide an overhead projector capable of preventing the deterioration of a polarizing plate installed to prevent the displayed content of a liquid crystal display unit from being doubly projected in an overhead projector capable of projecting the displayed content of the liquid crystal display unit. CONSTITUTION:This overhead projector is constituted by providing a light source 15, a mirror Fresnel lens 12, a condensing lens 16, and the polarizing plate installed on the front or rear side of the lens 16 so that it may be separated from the liquid crystal display unit and preventing a double image from being projected; and a photosensor 30 is installed on the polarizing plate. When the photosensor 30 detects light having intensity equal to or above specified value, an alarm 40 is actuated so as to give an alarm that the polarizing plate 24 is forgotten being detached, and the polarizing plate is prevented from being deteriorated by strong light. |
