Managing effective use of overhead projectors (OTP/OHPs) in education

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Managing effective use of overhead projectors (OTP/OHPs) in education
An overhead projector (OHP), like a film or slide projector, uses light to project an enlarged image on a screen. In the overhead projector, the source of the image is a page-sized sheet of transparent plastic film (also known as 'foils') with the image to be projected either printed or hand-written/drawn. These are placed on the glass surface of the projector, which has a light source below it and a projecting mirror and lens assembly above it (hence, 'overhead'). They were widely used in education and business before the advent of computer-based projection
Overhead projectors were widely used in education and business before the advent of computer-based projection
Educational uses of the overhead projector and its various strengths and weaknesses. Basic guidelines for using the overhead projector effectively are then offered, which include ways to avoid some common problems. Finally, detailed guidelines for designing and producing overhead projector software are provided which cover the following topics:
 (1) The two basic forms of overhead projector software the continuous roll and the single transparency--and their respective
 (2) Basic principles for designing overhead projector transparencies;
(3) Producing the transparencies by hand, with typewriter, from opaque originals, or using a computer-based system; and
 (4) Display techniques such as use of progressive disclosure, overlays, and animation. An annotated list of two items recommended for further reading is included. (MES)
The overhead projector facilitates an easy low-cost interactive environment for educators. Teaching materials can be pre-printed on plastic sheets, upon which the educator can directly write using a non-permanent, washable color marking pen. This saves time, since the transparency can be pre-printed and used repetitively, rather than having materials written manually before each class.
The overhead is typically placed at a comfortable writing height for the educator and allows the educator to face the class, facilitating better communication between the students and teacher. The enlarging features of the projector allow the educator to write in a comfortable small script in a natural writing position rather than writing in an overly large script on a blackboard and having to constantly hold their arm out in midair to write on the blackboard.
When the transparency sheet is full of written or drawn material, it can simply be replaced with a new, fresh sheet with more pre-printed material, again saving class time vs a blackboard that would need to be erased and teaching materials rewritten by the educator. Following the class period, the transparencies are easily restored to their original unused state by washing off with soap and water.
LCD overhead displays[
In the early 1980s–1990s, overhead projectors were used as part of a classroom computer display/projection system. A liquid-crystal panel mounted in a plastic frame was placed on top of the overhead projector and connected to the video output of the computer, often splitting off the normal monitor output. A cooling fan in the frame of the LCD panel would blow cooling air across the LCD to prevent overheating that would fog the image.
The first of these LCD panels were monochrome-only, and could display NTSC video output such as from an Apple II computer or VCR. In the late 1980s color models became available, capable of "thousands" of colors (16-bit color), for the color Macintosh and VGA PCs. The displays were never particularly fast to refresh or update, resulting in the smearing of fast-moving images, but it was acceptable when nothing else was available.
The Do-It-Yourself community has started using this idea to make low-cost home theater projectors. By removing the casing and backlight assembly of a common LCD monitor, one can use the exposed LCD screen in conjunction with the overhead projector to project the contents of the LCD screen to the wall at a much lower cost than with standard LCD projectors. Due to the mirroring of the image in the head of the overhead projector, the image on the wall is "re-flipped" to where it would be if one was looking at the LCD screen normally.
verhead projectors were once a common fixture in most classrooms and business conference rooms in the United States, but in 2000s they were slowly being replaced by document cameras, dedicated computer projection systems and interactive whiteboards. Such systems allow the presenter to project video directly from a computer file, typically produced using software such as Microsoft PowerPoint and LibreOffice. Such presentations can also include animations, interactive components, or even video clips, with ease of paging between slides. The relatively expensive printing or photocopying of color transparencies is eliminated.
The primary reason for this gradual replacement is the deeply ingrained use of computing technology in modern society and the inability of overheads to easily support the features that modern users demand. While an overhead can display static images fairly well, it performs poorly at displaying moving images. The LCD video display panels that were once used as an add-on to an overhead projector have become obsolete, with that combination of display technology and projection optics now optimally integrated into a modern video projector.
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