Overhead projector
From Free net encyclopedia
Image:OHP-sch.JPG 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.
Transparencies are placed on top of the lens for display. The light from the lamp travels though the transparency and into the mirror where it is shone forward onto a screen for display. The mirror allows both the presenter and the audience to see the image at the same time, the presenter looking down as if writing, the audience looking forward at the screen.
Overhead projectors were once a common fixture in most classrooms and business conference rooms, but today are slowly being replaced by larger computer monitors, dedicated computer projection systems and interactive whiteboards. Critics feel that there are some downsides as those are more prone to failure and have a much steeper learning curve than a standard overhead projector. While a computer projection system eliminates the need to create hard copy transparencies of the slide show presentation; many presenters make both in case the computer hardware fails.
Contents |
History
The overhead projector was developed during World War II to facilitate the training of servicemen. It began to be widely used in schools and businesses in the late 1950s and early 1960s. A major manufacturer of overhead projectors in this early period was the company 3M.
References
501 Ways to Use the Overhead Projector by Lee Green (ISBN 0-87287-339-0)
Pop culture reference
"Farewell to Overhead": In 2005 the group monochrom created a melancholic electro pop song about the "dead medium" overhead projector and adolescence/socialisation. [1]
See also
- A related type of the projector is the opaque projector.
- Projector for a directory of projector typesde:Tageslichtprojektor