Manufacturers : Presentation equipment : Overhead projectors

Overhead projectors are devices which produce magnified images on a screen or wall of indicia-bearing transparencies, typically clear plastic sheets including textual and/or graphical information. An overhead projector is used to project an enlarged image recorded on a film onto a projection screen. An verhead projector projects enlarged images onto a screen from a transparent original such as a transparency or a liquid crystal panel. Overhead projectors are often used on conferences, lectures and educational or presentation meetings to project images and drawings recorded on transparent sheet materials, such as chart films, on a remote screen standing vertically and located remote from the overhead projector. An overhead projector generally has a structure in which an image projection sheet on which an image for projection is formed is placed on a stage, the image on the image projection sheet is enlargedly projected on a screen through a projection lens by the light emanating from a light source illuminating the image projection sheet. An verhead projector is provided with a projection lens for projecting images onto a screen from a transparent original, and a reflection mirror for reflecting the light from a light source toward the screen. A Fresnel lens is commonly disposed inside the stage for converging light from the light source on the projection lens. Genarally, there are two types of overhead projectors differing in position of the light source: the reflection type and the light transmission type. Transmissive overhead projectors are generally comprised of a base having a transparent stage area, a light source inside the base, a projection head mounted above the stage, and a condensing lens system located near the stage for directing the light towards the projector head. Transmissive projectors have the light source below the stage and an overhead arm carrying a projection lens and a mirror. Light is focused and transmitted through the transparency on the stage toward the projection lens which is located by the arm over the stage and reflected by the mirror. The light source of the light transmission type is arranged beneath the stage, on which a Fresnel lens is placed to support the original material. Reflective projectors carry the light source in the overhead arm and have a reflective surface below the stage. Light shines down onto the stage and is reflected back up through the material which is placed on the stage. The light source of the reflection type is arranged in a unit incorporating the projector head, and the stage has a fresnel mirror that supports the original material.

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