zero-science: projector-types,specification details.

projector

Types of projector:

- dlp projector
- lcd projector
- video projector
DLP Projector-
                                DLP technology is based on an optical semiconductor called a DMD chip (Digital Micromirror Device), which was invented in 1987 by Texas Instruments (can't remember the guy's name). The way it works is that a DMD chip is made up of millions of tiny mirrors, that can rotate at a 10 degrees angle (12 degrees on better models). These mirrors are literally capable of switching on and off thousands of times per second and are used to direct light towards and away from a dedicated pixel space. The length of time a pixel is on/off determines the level of gray seen in the pixel. Completely on is lightest (white) and off is darkest (black), although neither is ever pure white or black. The current DMD chips can produce 1024 shades of grey. However, colour is still to be added.
DLP Projection: (note its an old image thus only 3 colour segments)

On a DMD chip, colour is added using a colour wheel. This is a wheel that spins round anything from 150x per second to 250x and more. Most of the cheaper models will be made up of a 4 segment colour wheel. This will be

Red/Green/Blue and usually a clear segment. As light is passed through a point on the spinning colour wheel the mirrors switch in accordance with the light. 4 segment colour wheels can produce an effect that is known as a rainbow. This is when the projector, in effect, struggles to change between all the colours quick enough, and along a line, the viewer may see a rainbow effect

6 Segment colour wheels are not affected in this way as badly as 4 segment colour wheels. Note that most viewers will not notice any rainbow effects, but some may. 6 Segment Colour wheels tend to spin faster and are made up of 2 sets of Red/Green/Blue segments thus enabling faster changes between the colours. Some projectors like the Marantz system (Absolutely amazing projector) have 7 segment wheels with an extra dark green colour which can give even greater contrast rations (3000:1+). This is achieved with the Texas Instruments DMD HD2 chip, which is found in some more expensive projectors. A new feature due out in 2004 sometime is the xHD3 technology. It will take the single-chip technology to even greater heights by adding a new rear coating to the mirrors and eliminating more of the latent brightness when in the off position. Another upcoming technology is called Sequential Color Recapture (SCR) where DLP systems will replace the traditional color wheel with essentially, a Spiral of "Archimedes" RGB color pattern. This new technology has been mathematically projected to rival the current quality of 3-modulator DLP Cinema systems.

DLP is the future of Home Cinema Quality projection. However, due to the high cost of manufacturing the chips, LCD and CRT are more viable options on the cost front. The potential drawback of this single-chip DLP technology is that in any given instant, the picture on the screen is not the total image, but is instead rapidly alternating between images consisting of the individual red, green, and blue colors. Thus the eye and the brain play the last critical role in making single-chip DLP projectors work, by combining or averaging or integrating the picture, so that the viewer perceives the desired image and not the rapidly flashing momentary components of the image.

A problem with DLP can also be light leakage around the mirrors ending up with a halo effect on some scenes. This has been addressed with the new Dark chip (DDR) which has a dark coating underneath the mirrors.

LCD Projector-

The Basics A LCD projector works similarly to other projectors in that it projects light through a filter to create an image. However, there must be a differentiating factor between a slide projector and an LCD projector. This difference comes from the fact that LCD projectors provide some of the crispest and clean images possible with a projector. This is done similarly to many other digital imaging devices, using only three colors per pixel: red, green and blue.

The Components of an LCD Projector The filter in an LCD projector is the actually LCD screens, of which there are three. These three screens are situated at right angles to each other and form three sides of a square. The fourth side is left open to let out the light to be projected. These LCD screens have light shown through them to create an image. Each LCD screen receives one of the three colors of light used. Hence, there is one screen for blue, one for red and one for green. The red, blue and green light for the three LCD screens is produced by a metal halide lamp, then filtered and reflected into the LCD screens. As the final touch on the device, there is a prism in the center of all three LCD screens that focuses the three images into one and projects that image through a lens and onto a screen

How an LCD Projector Creates The Image To create the image, red, blue, and green light must be shown through their respective LCD screens, then brought together in a prism to form an image. This is done with the use of mirrors. As the light propagates from the metal halide lamp, it is shown through a dichroic mirror. This mirror only lets the red light through it but reflects the rest of the light. The rest of this light goes through another dichroic mirror that only lets the blue light through but reflects the green light. Hence, the red light is shown through a mirror and reflected into its LCD screen while the green light is reflected into its LCD screen. Then, the remaining blue light that passed through the second dichroic mirror is reflected a couple times on its LCD screen. Finally, the three colors are filtered by the grayscale images on the LCD screens to form the desired image, overlapped by the prism and projected onto a screen.

here is a simple LCD projector....

check this out:

DIY Multimedia LED Projector (video manual) by newtonn2