For the latter purpose, the projector includes a mirror just before or after the focusing lens to fold the optical system toward the horizontal. However some differences are necessitated by the much larger size of the transparencies used (generally the size of a printed page), and the requirement that the transparency be placed face up (and readable to the presenter).
They were widely used in education and business before the advent of video projectors.Īn overhead projector works on the same principle as a slide projector, in which a focusing lens projects light from an illuminated slide onto a projection screen where a real image is formed. These are placed on the glass platen of the projector, which has a light source below it and a projecting mirror and lens assembly above it (hence, "overhead"). In the overhead projector, 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. Overhead projector in operation during a classroom lessonĪn overhead projector (often abbreviated to OHP), like a film or slide projector, uses light to project an enlarged image on a screen, allowing the view of a small document or picture to be shared with a large audience. JSTOR ( February 2008) ( Learn how and when to remove this template message).Unsourced material may be challenged and removed.įind sources: "Overhead projector" – news Please help improve this article by adding citations to reliable sources. This article needs additional citations for verification.
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