Projection Systems: Projectors to Panels, Choices Abound
Elizabeth Greenfield · T.H.E. Journal Technological Horizons in Education · 1991
Projection systems come in various shapes and sizes. Differing from overhead projectors, these units interface directly to computer to display text, graphics, animation and more. Examples of popular projection systems include CRT-based projectors, rear-projection systems, LCD panels and newer hybrid items that offer innovations in both form and function. Many protection systems will display information from videodiscs, VCRs, camcorders and other input devices. Projection systems can also double as administrative tools useful for presentations and inservice training, seminars and workshops. * Video/data Projectors There are three types of machines used for video/data projection: light-valve projectors, LCD-based projectors and CRT-based units. General Electric manufactures the Talaria LV8000 MP Data/Video Projector, light-valve unit that produces picture from 6' to 30' wide. The unit interfaces with LIP tO 16 different video and computer formats, allowing it to display images from any computer operating within 15Khz to 36Khz, such as PC, PS/2 and Macintosh II computers. The Talaria LV8000 produces single optical light path so no convergence adjustments are required. Shipped with five additional, interchangeable lenses, the unit can be placed up to 84 feet away from, yet still project clearly onto, 9' x 12' screen. The University of Michigan's Center for Performing Arts and Technology purchased Talaria LV8000 because it handles various applications, screen sizes and throw distances. The Talaria is used in the center's video dance programs, which are presented in large auditorium that accommodates up to 1,400 people. Colorful video and computer graphics images are displayed on 23'-wide screen positioned behind the dancers. The end product is, according to the center's video technology consultant, a spectacular multimedia performance. LCD-based projectors offer low-cost alternatives for video and data projection. Sharp Electronics produces three second-generation projectors that incorporate three convergence-free, solid-state LCD panels rather than CRT tubes; built-in 20 to 100 zoom lens; switch for rear projection; industrial BNC-video connectors; and connections for standard video sources including computers. The XG-1500U, ceiling-mounted LCD projector, weighs 23.4 pounds, has built-in analog RGB input, and can be operated by wireless remote. Standard CRT-based projectors, also known as three-gun machines, are the most prevalent data projectors in education. They comprise three cathode-ray tubes-one each to display red, green and blue light. One drawback to these units is that trained technician must perform convergence adjustments each time the unit is moved to ensure sharp, focused images. To remedy this, several CRT-based projectors now contain digital convergence technology to simplify the process. These projection systems produce certain amount of lumens, measurement of light output in which more is better (i.e. brighter). In addition, high levels of horizontal resolution offer clearer pictures. computer platforms can be determined by comparing the horizontal scan frequency range of the computer to that of the projector. For example, Apple II, IIe and IIGS computers operate at 15Krz; projectors running at up to 36Khz will support these computers plus DOS-based machines with RGB analog or TTL graphics. The same projectors will also accept video input signals like NTSC, S-VHS, PAL and SECAM. Computers with CGA, EGA, VGA and Super-VGA graphics plus Macintosh II computers are supported by projection systems that achieve 50Khz. Several companies manufacture CRT-based projectors that achieve maximum horizontal scanning frequency of 37Khz. Panasonic's A/V Group makes the PT-200, 120 color video/data projector the company claims will automatically and continuously adjust to the input signal it receives. …