what is an overhead projector

An overhead projector is a device that projects an enlarged image on a screen or wall using light. It is a basic but reliable tool used to display images, allowing the view of a small document or picture to be shared with a large audience. The source of the image is a page-sized sheet of transparent plastic film, also known as "foils" or "transparencies," with the image to be projected either printed or hand-written/drawn. The transparency is placed on the glass platen of the projector, which has a light source below it and a projecting mirror and lens assembly above it. The light from the projector passes through the transparency and is focused by the lens onto a screen or blank surface. The mirror flips the image of the transparency so that it is projected the right way. Overhead projectors were widely used in education and business before the advent of video projectors. They were once a common fixture in most classrooms and business conference rooms in the United States, but in the 2000s they were slowly being replaced by document cameras, dedicated computer projection systems, and interactive whiteboards.