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The theory behind projection
The principals that make projection in general possible are very simple in
concept. You need simply 4 requirements to be met: a light source, the brighter
the better; some form of imagery medium, film or LCD it's all the same
conceptually; a focusing mechanism to help provide a crisp image; and finally a
display medium. There are many ways of accomplishing each of these
requirements. We will be glancing over them and providing some examples that
could fulfill the requirements for our LCD Projector.
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The Light Source - The LCD Projector Bulb
Back in the day traditional carbon arc were used in actual film based
projection, but modern xenon arc lights are now more common. Xenon's were
introduced in the 1950s, they are safe and easy to use, and are relatively
cheap. Most all
LCD
based projection use Xenon or filtered Metal Halide, based light sources.
Commercial or non
DIY
projectors can have bulbs that are very very expensive, often in excess of
$500.00 for a bulb that usually can only last for 2000 hours. All bulbs are
sensitive to shock, getting bumped too hard can be a costly mistake. So what
are the most common practical light sources?
Xenon Light Source
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$20 - $150
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Construction Utility Lights
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$50 - $250
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Modified Automotive Head Lights
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$10 - $40
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Overhead Projectors
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$10 - $150
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Coustom Solution
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$20 - $100
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The Imagery Medium - The LCD Projector Panel
Historically, cellulous based films were used as the imagery medium.
Light passing threw the film, and interacting with a shutter created the
viewable content.
LCD
projectors act on a similar principle. Light passing threw the
LCD
creates the viewable content. There are many ways of using
LCD's of many verities. Now,
here is where I have to return to the point that this may not be the first
how-to article. There are a lot of articles with little to no foresight in this
type of project. Picking a cheap
LCD
monitor off the shelf for instance is a bad idea. Normal
LCD
(Liquid Crystal Display) are not designed to be used in high-heat environments.
Using a cheap
LCD
panels can result in nothing more than an expensive paperweight. The seal
around the edge of the monitor can crack or become damaged allowing the liquid
layer between the layers of glass to dry out and become worthless. Secondly,
there are many
DIY
attempts to fulfill the requirements of an inexpensive monitor with a small (4
inch or so)
LCD
panel. The problem with this is most small monitors have only 250 or so lines,
so you may as well throw the image quality out the window. These methods do
work, they just are not very effective compared to similarly priced solutions.
15"
LCD
Monitor
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$170 - $250
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5 - 6 "
LCD
Monitor (without
svga
support)
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$70 - $130
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5 - 6 " LCD Monitor (with
svga
support)
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$180 - $270
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LCD
Projection Pannel
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$20 - $90
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