A device consisting of a light source, a transmissive or reflective platform and a focusable lens assembly. An OHP is designed to project images from transparencies up to 12" x 12" (usually A4) onto a screen. Although regarded by many as 'old technology,' the simplicity and ease of use of the OHP offers numerous benefits. It allows pre-prepared transparencies to be used and enables a presenter to command attention by writing or annotating in colour on to sheets of clear film in real time. In many cases it the OHP is being replaced by the video visualiser (electronic OHP) which transmits images of solid objects, documents and written notes to an electronic projector or monitor screen via a fixed CCD video camera.
A device consisting of a light source, a transmissive or reflective platform, and a focusable lens assembly. An OHP is designed to project images from transparencies onto a screen. LCD projection panels are designed to be used with transmissive OHPs and work best with OHPs that produce at least 3,000 lumens. Since 5% to 10% of the light that shines through an LCD panel gets onto the screen, a 3000 lumen OHP will produce an image of 150 to 300 lumens. Transmissive OHPs are fairly bulky (bigger than many projectors). Reflective OHPs are fairly portable but are not useful with LCD projection panels.
A device consisting of light source, a glass platform and a focusable lens assembly, designed to project to a screen, images from transparencies. Overhead projectors for LCD panels are particularly bright, and start at about 3000 lumens, or about 2 to 4 times as bright as most older overheads.
In ancient history, overhead projectors were used to give presentations. They involved static pages of see-through "paper" on which black images were printed. Historians suggest ancient presenters even used marking pens to write on these transparent pages.
An overhead projector is a display system that is used to display images to an audience. They typically consist of a large box containing a very bright lamp and a fan to cool it, on top of which is a large lens that collimates the light. Above the box, typically on a long arm, is a mirror that redirects the light forward instead of up.