Projectors are devices that use a light source to display images of video on a screen for the purpose of group viewing. Some of the earlier types of projection devices include slide projectors and overhead projectors. Their use has been in decline in recent years since they are only able to project still images. The invention of new technology has corrected this problem. Video projectors are often used for such applications as use in home theaters and for business presentations.
A slide projector is a mechanical device that displays still images either on a screen or wall. It is made up of four separate parts that allow images to be projected. A fan-cooled electric bulb is responsible for providing the light necessary to project an image. A special condensing lens along with a reflecting device is used to aim the image while a holding mechanism secures the slide and focusing lens.
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An overhead projector is a device used to share images with an audience by projecting images on a screen or wall. They are fairly bulky devices that are usually set on a dedicated stand or rolling cart. The inner workings of the outdated device include a bright lamp with an accompanying fan to cool it down, a large lens that filters the bulb's light. This is all contained in the bottom piece of the projector in a large metal "box." The light from the lamp is shot upward where it hits a mirror and lens supported by an arm of sorts that reflects the image frontward.
Video projectors use very powerful electric bulbs to project their moving images and often allow users to make adjustments to size, picture quality, and many other settings by using manual controls and controls through an onscreen menu. Some of the most common types of video projectors are LCD and DLP projectors. LCD projectors use liquid crystal display light gates to reproduce moving images on a screen. It is the simplest and most affordable type of video projector. DLP video projectors incorporate Texas Instrument's digital light processing technology. These video projectors usually use one or two light valves to produce a crystalline image.
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