Tips for the user. projectors. Optical design. Homemade LCD projector for home theater Projection work

Of course, we all want to watch movies on big screen. The sizes of plasma and liquid crystal panels offered on the market are increasing, but their cost is also increasing, sometimes reaching frightening values. The problem can be solved by purchasing a projector, organizing a real cinema at home.

Meet the Projector

A multimedia projector is a device for projecting onto a large screen information coming from an external source - a computer, VCR, CD and DVD player, video camera, etc. Some models have a memory card slot and/or USB port, which allows you to produce video without using a computer. As a rule, a projector has both a computer and a video input, but it’s a good idea to inquire about the set of inputs before purchasing a device: there are models with only video inputs or only with computer inputs.

The most important characteristics of a multimedia projector include resolution and luminous flux. Additional characteristics of projection devices include contrast, uniformity of screen illumination, the presence of a ZOOM lens, as well as the number and types of input and output connectors. When choosing a projector for outdoor presentations, an important parameter is the weight of the device, but for stationary use as part of a home theater, this parameter fades into insignificance.

Resolution, or resolution, characterizes the granularity of the video image created by the projector and is determined by the number of luminous elements - pixels of the liquid crystal display (LCD) or micromirrors. The higher the resolution, the smaller the size of the luminous elements, the higher the quality of the image on the screen and, naturally, the price of the device.

If you are purchasing a projector primarily to display DVD movies and television programs, it is advisable to choose a model whose playback element has a Home Cinema format with an aspect ratio of 16:9.

The luminous flux produced by projectors is measured in ANSI lumens. This unit characterizes the average value luminous flux projector over nine zones evenly distributed over the screen area, was introduced in 1982 by the American National Standards Institute (ANSI). In 2009, leading projector manufacturers such as Epson and Sony began to specify new characteristic— color brightness of the projector. Color brightness differs from ordinary brightness in that it is measured not by the white field of the screen, but by three color zones - red, green and blue. Thus, color brightness (CLO - Color Light Output) allows you to evaluate not only the nominal brightness, but also the color rendering quality of the projector.

Most modern multimedia projectors are equipped with zoom lenses with variable focal length (the so-called ZOOM), which allow you to change the size of the image on the screen without moving the projector. In the most advanced models, the lenses are equipped with electric drives, and image adjustments are made from the remote control.

It’s worth taking a look at the panel with connectors, among which, as a rule, there are one or two analog (RGB) computer inputs, one RGB output for parallel connection of a computer monitor and several ports for connecting video signal sources, both composite (low-frequency) and more high-quality S-video signal. The most advanced models also have separate inputs for component video, providing best quality images, for digital computer signal, as well as digital inputs DVI-D, DVI-I, HDMI with x.v.Color support in versions 1.3a and higher, or MiniDisplay Port.

Do you want LCD or DLP?

Among the technologies used today for displaying images on a projection screen, two are most widely used: LCD technology with a matrix on liquid crystals (Liquid Crystal Display) and DLP technology for digital light processing (Digital Light Processing).

In an LCD projector, the light from the lamp is divided into red, blue and green light streams, each of which passes through its own liquid crystal matrix, after which a dichroic prism reconnects the streams, and the lens projects a full-color image onto the screen. The presence of three independent matrixes for each color is emphasized by the often used abbreviation 3LCD.

LCD projector circuit:

1 - light source (mercury lamp), 2 - dichroic mirror, 3 - HC panels,

4 - dichroic prism, 5 - lens, 6 - screen

The basis of the DLP technology proposed by Texas Instruments is a matrix of microscopic metal mirrors, the so-called DMD elements (Deformable Mirror Devices, that is, deformable mirror devices). The electric field that controls their position directs light from the mirrors to the screen, and the more often the flow of light from the mirror hits a certain point on the screen, the brighter it seems to us. You need to understand that we are talking about vibrations with a frequency of hundreds of thousands of times per second, so vibrations of mirrors and flickering light spots are not perceived by our eyes.

DLP projector circuit: 1 - light source (mercury lamp),

2 - filter, 3 - DMD chip, 4 - lens, 6 - screen

In projectors with one DMD chip, a disk with sectors of different colors (red, blue and green) rotates between it and the lamp, as a result of which the image becomes colored - but not on the screen, but in the viewer’s head. The flickering of colored sectors also causes the “rainbow effect” - when we see the red-blue-green components of any part of the picture. All this can cause eye fatigue when viewing.

In more “advanced” three-chip devices, the lamp light is divided by a prism, after which a beam of a certain color is directed to each chip. Having connected again, the light rays are directed to the screen, forming a full-color image on it. More expensive compared to single-chip models, such models transmit large quantity gradations of color and are less affected by the “rainbow” disease of the picture on the screen.

Which technology is better? It is hardly possible to answer this question unambiguously. Experts note that with the same lamp power, LCD projectors produce a brighter, more realistic and color-saturated picture compared to DLP models, however, the pixelation of the image on the DLP matrix is ​​less due to the closer arrangement of the elementary cells. Considering that both technologies are constantly improving, the dilemma of “LCD or DLP” will remain unresolved for a long time.

Without further ado, let’s first look at the new products in the family of LCD projectors, after which we’ll move on to their DLP opponents.

Epson for the anniversary of 3LCD technology

In 2009, Epson celebrates the 20th anniversary of 3LCD technology, the first projector based on which was created in 1989. On the eve of this glorious date, the company announced the release of the EH-TW5000 HD projector - flagship model with a resolution of 1080p. The projector has significantly improved performance, delivering bright images, crisp colors and accurate shadow reproduction. Featuring new D7 CFine 3LCD panels, advanced Epson DeepBlack technology and an improved E-TORL lamp that minimizes light leakage and guarantees high quality black color transmission, the projector's contrast ratio reached 75,000:1 for the first time. The model supports a 2.35:1 cinema screen format, which means you can watch movies without black areas at the top and bottom of the screen.

Epson EH-TW5000

The universal stylish design and black body of the Epson EH-TW5000 projector allows it to be harmoniously placed both in a room with a classic setting and in a modern room.

Samsung: not like everyone else

The teardrop-shaped silver body of the new Samsung SP-D400 projector sets it apart from the usual “boxes”. On the side edges of the device there are cooling radiator cells that ensure uninterrupted operation and reliability even during long presentations. But the main advantage of this model is its high brightness, equal to 4000 ANSI lumens. This indicator allows you to use the projector in any conditions, even where it is difficult to achieve darkness.

Samsung SP-D400

The high contrast level of 3000:1 and XGA resolution of 1024x768 are also responsible for the excellent picture quality. The model features an ultra-low noise level - only 26 dB.

The new product offers the user maximum freedom of choice of source thanks to a full range of inputs: HDMI, PC, S-Video, VGA, composite and component. The projector is certified to be compatible with Windows Vista and offers one of the best value for money in its class.

Sanyo: richness and realism

The well-known Japanese manufacturer of projection equipment - Sanyo - introduced a new Full HD LCD video projector PLV-Z3000 with a contrast ratio of 65,000: 1. This contrast ratio means not only that the projected image will be as rich, bright and realistic as possible, but also solves the main problem The problem with all 3LCD projectors is poor black color display.

Sanyo PLV-Z3000

Another important indicator for a home projector is the noise level. In the new product it is minimal - 19 dB, and you simply will not hear any noise from the lamp cooling system.

The projector's brightness (1200 ANSI lumens) is optimized for home theater use. In addition, the advantages of the new product include double ZOOM, an improved Lens Shift lens shift mechanism and an automated protective curtain that protects the projector lens from dust.

You can connect a variety of video sources to the projector: Blue-Ray/DVD player, computer, game console etc.

Acer guarantees clarity

The number of new products based on DLP matrices appearing on the market serves as further confirmation of the fact that before the question “which technology is better?” still very, very far away.

Thus, Acer Corporation introduced the ultra-short throw DLP video projector S1200. The new product features optimal lamp brightness, which ensures an exceptional level of brightness of the projected image, regardless of operating conditions. The model also attracts attention with its special style: shiny black surface and rounded edges of the case.

Acer S1200

Continuing to improve ColorBoost image optimization technology, the company has developed ColorBoost II, which provides new benefits for viewing dynamic and bright scenes. The projector also features Ultra-Short Throw Distance technology to project clear images close to the screen.

Acer's EcoProjection environmental solution reduces the device's standby power consumption by up to 50%. EcoProjection also includes Acer ePower Management for personalized power saving settings.

The projector supports NTSC, PAL, SECAM, HDTV and EDTV input signals, and its connectors, including D-sub and HDMI, provide the ability to connect to a PC, laptop, DVD or game console.

Pioneer - stability example

The word Kuro means "black" in Japanese. The smooth black lacquered design of the Pioneer Kuro KRF-9000FD DLP projector is consistent with the entire line of Pioneer Kuro home theater products. But Kuro isn't just about design: it delivers stable images with an impressive 30,000:1 true-to-life contrast ratio for deep blacks. The image is clear, accurate and natural.

You can fine-tune the colors to suit your tastes and the content you're viewing. The projector has a gamma control function that allows you to manually set the brightness of the image to suit your personal preferences.

The model displays extremely high-definition images with a progressive scan resolution of 1920 x 1080p and a speed of 24 frames per second. This means it is able to accurately reproduce HD sources such as Blu-ray Discs. All digital video signals are transmitted via HDMI directly from the source to the screen without conversion or compression.

The device has a universal motorized lens: you can vary the image size to get the one you prefer, regardless of the size of the room. Lens shift is ±80% vertical and ±34% horizontal.

Sony: new technologies in action

Sony brings us a new product: the VPL-VW200 home theater projector, which features 1080p resolution, high frame rate SXRD matrices, a Carl Zeiss Vario-Tessar lens and a contrast ratio of 35,000:1.

Three 1920 x 1080 sensors deliver 1080p resolution and cinematic smoothing, while Motionflow Dark Frame Insertion technology ensures fast-moving scenes are seen more clearly. Advanced Iris 2 technology allows you to manually adjust contrast, BRAVIA Engine Pro technology provides crisp, realistic images, and x.v.Colour technology delivers vibrant, rich colors.

Sony VPL-VW200

The Carl Zeiss Vario-Tessar lens is extremely high in resolution and sharpness and optimizes the overall image, while its adjustable shift makes adjustments easy (vertical: 65% up or down, horizontal 6.7% left or right).

BRAVIA Theater Sync technology allows you to control the projector and your entire home theater system with the touch of a button. The Sony VPL-VW200 projector features extensive connectivity options, including two HDMI inputs for connecting high-definition sources such as BlurayDisc.

Canon raises the bar

With the introduction of the XEED WUX10, Canon ushered in a new era in the world of portable projectors. With WUXGA resolution (1920 x 1200 pixels) and support for Full HD video (1080p), the projector sets new standard in branch.

Canon's proprietary LCOS technology has made it possible to combine the advantages of DLP and LCD projectors. Projected images are of superior quality and detail-rich, without the unwanted "grid" and "rainbow" effects associated with traditional technologies.

Canon XEED WUX10

Canon's unique AISYS (Aspectual Illumination System) optical system optimizes the light path from the lamp and provides two key benefits: the highest level of brightness (3200 lumens) and
contrast ratio (1000:1).

The result is images with rich colors and deep blacks, even in well-lit rooms.

The model supports the 16:10 aspect ratio characteristic of new computer monitors—a picture in this format fits entirely within the projector frame without compression or panning. The 1.5x zoom lens allows you to place the projector in any convenient location, ensuring ideal geometric proportions throughout the entire field. A 10:0 lens shift ratio makes installation much easier, while DVI and HDMI inputs allow direct connection to the latest video devices such as personal computers and Blu-Ray Disc players.

Sharp for home theater

The new Sharp XV-Z15000 model is a high-quality Full HD home theater projector with a real High Definition resolution of 1920x1080. The DLP projector provides a very high contrast ratio of 30,000:1 and a brightness of 1600 ANSI lumens, which allows for high-quality images. High contrast levels allow you to see the smallest differences between the darkest and lightest colors, and also provide the highest level of black reproduction.

Sharp XV-Z15000

The projector's color wheel is six-speed and six-segment. There are six image display modes, there is the possibility of spherical and cylindrical image correction, as well as its rotation clockwise and counterclockwise.

The use of dual iris technology allows you to change brightness and contrast with just one button, and also creates an immersive effect during the display. For maximum convenience, the projector has a CEC (Consumer Electronics Control) technology function, using which the device can be automatically turned on when you press the Play button on the video player connected to the projector via HDMI cable. In this case, the video player will automatically turn off when the projector itself is turned off. The projector is reliably protected from dust, dirt and smoke.

For reference

SXRD is a registered trademark of Sony for products using LCoS (Liquid Crystal on Silicon) technology. This imaging technology is the third most common after DLP and 3LCD (LCD) technologies, but has a significantly smaller market share.

The operating principle of a modern LCoS projector is close to 3LCD technology, but unlike the latter, it does not use transmissive LCD matrices, but reflective ones (this LCoS is already related to DLP technology).

Text: Alexander Pustynny

Watching movies at home on the big screen is a very common desire. But its implementation is significantly expensive for most dreamers. Otherwise, they would simply buy either a projector or a TV. But those who understand the design of electrical appliances are quite capable of independently making a projection device for a home theater. This will be discussed further.

A little theory

First, let's look at the diagram of the correct projector. Obviously, not everyone can make such a device. If only because you will need several accurate and high-quality factory-made optical parts:

• lens;
• lenses.

The uniformity of light distribution on the screen will depend on them. The light must enter the lens at the correct angle. If you do not know the optical characteristics of the lens and lenses, all distances can be determined experimentally.

The image source in the projection device is a liquid crystal matrix. They work for the light. Moreover, each pixel on the screen is projected with increasing size. Therefore, the original image should be as clear as possible. The more pixels the better. The so-called FULL HD is 1920x1080 pixels. The brightness of the projection lamp will determine the maximum screen size on which you can watch movies with acceptable brightness and contrast.

The simplest projector

If the reader owns a smartphone or tablet with a bright screen and a resolution close to FULL HD, and also dreams of watching movies on a big screen, he can try to make a simple device from a box, a lens and his gadget. The box-case must be in any cross section larger than the gadget, and the diameter of the lens is comparable to the size of its screen. But the distance to the screen will depend on its focal length. The idea is simple:

• a hole for the lens is cut in the box;
• A gadget is placed inside, which can be brought closer or further away from the lens.

The gadget is installed in a mandrel that is convenient to move in the box. For mandrel, another box with smaller sizes. Reflection of light from the walls of the boxes should be minimal. To do this, it is best to cover the surfaces with black velvet applique paper. Or paint it with matte black paint. Instead of paint, you can use thick black shoe polish. It is best to place guides between the walls of the boxes, especially when using velvet paper. They will protect painted surfaces from rubbing.

That's the whole projector. See its details in the images below.

Painted box
The lens is applied to the body and outlined with a pencil.
A hole is cut along the line from the pencil with a sharp knife.
A lens is inserted into the hole and glued along the contour

We place the carriage inside the housing box and use the projector

The result we see on the screen greatly depends on the size of the image on it. If the size is reduced, the brightness and clarity of the frame will improve. The image quality in this simple projection device is at the “better than nothing” level. But the reason for this is obvious - a higher brightness of the image source and additional optics are required.

High-quality homemade projector

Next, we’ll tell you how to make a projector with your own hands, observing all the requirements. You need to start by disassembling the gadget. It is disassembled while maintaining its functionality so that the liquid crystal matrix of the screen is accessible for illumination by an extraneous light source. If you can't do this, then building such a projector is not for you.

Parts used:

1. LED power supply board;
2. LED 100 W (a light source with minimal dimensions is advantageous);
3. fan power supply board;
4. fan control board;
5. intermediate lens;
6. output lens;
7. gadget control panel via Wi-Fi;
8. two intermediate Fresnel lenses;
9. liquid crystal matrix from the gadget.

Heat sink mounted LED



Demonstration of the effectiveness of a Fresnel lens.
An intermediate lens is placed between the LED and the Fresnel lens to reduce light loss




Elimination of projection distortions by suspending a matrix with lenses with horizontal and vertical deviations

And here is the result of the work done. The distance to the screen is 4 meters, the diagonal of the frame on the screen is 100 inches. Everything is clearly visible.

Based on a slide projector

But there is an easier way to create a projector. To do this, you can use a projector for slides that are projected from a sheet of A4 paper (overhead projector). Since all the optics are already in stock, all that remains is to attach the image source to it. It could be a monitor matrix. It will have to be disassembled while still working. Because after installing the matrix in the projector, the monitor, as usual, is connected to the computer. It is best to use a projector that illuminates the slide rather than using reflected light.

What results from this hybridization of a monitor and a projector is shown in the images below.

That's all there is to do. If, of course, you have such a projector. The resulting visibility on the screen is shown in the image below.

The size and quality of the frame on the screen are very good. Moreover, there are projectors for projecting small slides that are comparable to a smartphone screen. They are cheaper. Therefore, you can buy a smartphone with a broken screen and a faulty projector for its matrix. And what should happen as a result is already shown above.

A projector is a complex mechanism with the whole system electronic boards, light elements and lenses

The question of how a projector works should concern everyone who owns such a device or regularly encounters it. Knowing the basic principles of operation of such equipment, you can successfully care for them and make proper adjustments. Regardless of the operating principle of the projection device and the technologies used in it, the basic device does not change. Only additional lenses, reflective surfaces, processors, etc. appear. There are two main components of the projector.

Video

The video was taken from the Internet on this topic to make it easier for you to understand the details.

The first is the lamp itself. In this case, the design of the projector does not determine the type of light element used: a discharge lamp with one base or with two contacts. The only difference between these lamps is the service life, which is measured in hours of continuous operation and the connection method. Well, the projector itself includes:

• audio and video processing board,
• lamp,
• light modulator board,
• diffuser,
• frame.

Projector lamp design

This is what a standard projector lamp looks like

Projector device | Introduction

We are all fascinated by the magical world of cinema. The atmosphere of the cinema allows you to completely immerse yourself in the action and feel the director’s intentions, feel a surge of emotions and even, to some extent, live the lives of the on-screen characters. Of course, hardly anyone will argue that one of the main aspects of such a strong impact is a bright, rich image large format. And today such a picture can only be obtained using projector– a device that uses a light source to project images onto a screen. It is worth noting that modern projectors- these are very high-tech devices, but the origins of the very principle of forming such a picture go back centuries. If we approach the issue quite simply, then the first spectators can be considered primitive people who observed moving shadows from fire on the vaults of caves. Then comes to mind the famous Chinese shadow theater, which uses what we might today call rear projection. And the first mass devices appeared only in the 17th century. They were called "magic lanterns", the inventor of which is considered to be the Dutch scientist Christiaan Huygens. The construction of a magic lantern was very simple: a light source was placed in a wooden or metal case, and images for projection were drawn on glass plates framed in frames. The light passed through the picture and optical system located in the front of the device and onto the screen.

The history of the magic lantern goes back almost three centuries, and all this time the design has been improved. For example, a reflector was added a little later to enhance the luminous flux, and in the 19th century the candle was replaced by an electric lamp. By the way, magic lanterns were often used by traveling performers, surprising the public with an unprecedented light spectacle. It is worth noting that such devices were also common in pre-revolutionary Russia, where they were used for educational purposes. Moreover, the slide projector, which we have loved since childhood, is the direct descendant of the magic lantern. It is also impossible not to mention the decisive role of this device in the invention of cinema, with the advent of which the magic lantern ceased to be so popular, however, laying the foundation for all projection technology.

The popularity of cinema led to rapid advances in equipment not only for filming, but also for playback, which continues to this day. Specialized devices for training have appeared, such as overhead projectors, which can still be found in schools. They were replaced by the first models of multimedia devices that could be connected to various video signal sources, and therefore used to demonstrate films outside cinemas. Further development of technology has made it possible to organize viewing, in no way inferior to cinema, at home. The idea of ​​a home theater has captivated film enthusiasts and fans and created a new surge of interest in the film production industry. In addition, massive demand for projectors became the reason for a significant reduction in the cost of technology and the development of truly affordable models. This, in turn, has made it possible to widely use projection equipment in other areas, such as education.

So that's it modern methods Projection image generation can be divided into three groups: emissive, such as CRT, transmissive, such as LCD, and reflective, such as LCoS and DLP. Each of them has its own characteristics, advantages and disadvantages, which determine the popularity of a particular system on the market.

Projector device | Basic projection technologies

CRT (Cathode Ray Tube Technology)

Although projectors, built on the basis of a cathode ray tube, were and remain quite rare devices; for a full review, their mention and place in the history of modern projection technology are very important. These devices can be confidently called the ancestors of home theaters, since they made it possible to form huge images even when no one had heard of liquid crystals or micromirrors. So, what is CRT? projector?

The operating principle of these devices is familiar to anyone who remembers old televisions or computer monitors. The cathode, located at the base of the electron beam gun, emits a stream of electrons that accelerates high voltage. An electromagnetic deflection system then focuses the beam and changes the direction of the charged particles, causing them to bombard the inner surface of a glass screen coated with a phosphor, which begins to glow when exposed to electrons. Thus, the electron beam, tracing each frame line by line, forms a picture on the screen. However, since such devices use monochrome vacuum elements, one kinescope is not enough to obtain a full color image. Therefore, in CRT- projectors Three tubes are installed, which are responsible for the formation of basic colors: red, green and blue. By the way, since such devices always require a large luminous flux, the screen diagonal of each kinescope can be up to 9 inches. Next, all three images are combined into a single whole on the screen using massive lenses and various analog distortion correction systems.

CRT technology diagram

As for the image quality, even by today's standards it can be called remarkable. Firstly, it has excellent color rendition. Secondly, the ability to reproduce low black levels, and, as a result, display a picture with high contrast. And thirdly, the ability to reproduce almost any input signal resolution. In addition, such projectors can change the geometry of the picture, leaving the number of image elements constant. However, it is worth noting that such capabilities are required only in special tasks, such as, for example, combining several images in flight simulators.

CRT- projectors– very quiet, since they practically do not use active cooling systems. And at the same time, they can work continuously for hundreds of hours, although, again, such an advantage is practically not required for a typical home theater. It is also worth noting that such image projection technology is more than time-tested, because its history goes back about fifty years, and, therefore, everything possible difficulties production and exploitation have long been overcome. By the way, such devices are still produced.

Unfortunately, despite all efforts, the brightness of the displayed image cannot be called record-breaking. In addition, such projectors are not very suitable for forming static images, since the phosphor covering the inner surface of the kinescope tends to fade over time, and still images formed over a long time leave phantom traces that are quite noticeable on other images. It is also worth noting that a rather complex system for combining three basic signals requires periodic calibration, which requires a high-class specialist.

Considering that modern technologies image playback large formats, driven by the fashion for three-dimensional images and the introduction of ultra-high definition standards, are developing at tremendous speed, CRT- projectors Compared to the current models, they look like dinosaurs: just as huge, heavy and outdated.

LCD (liquid crystal transmission technology)

The modern era of projection devices is already associated with this method of image reproduction. It is worth noting that the formula “the new is the well-forgotten old” is fully applicable to this case. According to history, the first attempts to create liquid crystal projectors date back to the early eighties of the last century. In fact, the idea was to replace the moving film and shutter in a film projector with an LCD matrix that displays the video footage. And by the middle of the decade, the first commercial samples appeared. Of course, these devices were not without drawbacks - typical indicators: 9 kilograms of weight with a luminous flux of no more than 300 lumens, low resolution and a noticeable grid of pixels - however, they served as the starting point for the development of affordable means of reproducing large-format images and, as a result, a whole direction of mass home cinemas.

So how does LCD work? projector? The operation is based on the property of molecules of a liquid crystalline substance to change spatial orientation under the influence of an electric field. However, much more important is the fact that light passing through the cell can change the direction of the plane of polarization. Moreover, by controlling the applied voltage, you can change this very direction. But what does this give for the formation of a picture? It's very simple: if you add polarizing filters before and after the cell, the polarization planes of which are mutually perpendicular, you can control the transparency of any image element. Of course, this representation of the operating principle is quite simplified, but once upon a time everything worked exactly like that. Now add control transistors, conductors, additional pixels for each color channel, appropriate color filters - and you get a color liquid crystal panel.

So, we have an array of dots located on a glass substrate (so that light can freely pass through the matrix), the transparency of which we can control. But it's not yet projector: We need a powerful lamp, a cooling system, control electronics, a power supply, a lens for projecting the image and a housing. At first glance, everything is quite simple, but the use of one matrix almost immediately revealed several serious shortcomings: overheating of the LCD panel, low contrast and a general deterioration in the quality of polarizing films under the influence of high temperatures. Since the potential of the new technology was very high, its further development led to the appearance in 1988 of a circuit with three matrices, which was called 3LCD.

This design solution has proven so popular that it is used in projectors still. What is its peculiarity? The fact is that, as you can easily guess from the name, three matrices are involved in the formation of the image. So, light from a source (usually a gas-discharge lamp) hits a system of dichroic mirrors that are installed in the optical block. Their task is to transmit light of a certain spectrum and reflect everything else. Thus, white light is divided into three streams, which form the basic colors of the image: red, green and blue. Each beam passes through its own monochrome matrix, which forms a picture of the corresponding color, and then all three components are combined using a special prism. The resulting image is projected through the lens onto the screen.

3LCD technology diagram

Further progress in technology, which made it possible to place all three matrices close to the prism, which in turn increased the accuracy of convergence three images. In addition, the introduction of polysilicon technology helped not only to increase the resistance of the LCD panel to thermal heating, but also to significantly reduce the size of the conductors and control transistors. Thus, the luminous efficiency of the matrices has significantly increased and the possibility of further increasing their resolution has emerged. In modern projectors microlens raster panels are also used, which direct the light flux through the transparent area and thereby provide additional gain in brightness. It is worth noting that the technological process continues to be improved to this day, since the limit of possibilities has not yet been reached.

So, the main advantages of image formation technology based on three LCD matrices include high image brightness, low weight of the structure, easy setup and operation, as well as the ability to project images of very large formats. As for the disadvantages, they usually include the large distance between the pixels, which is a consequence of the need to place conductors and control transistors between the cells. This leads to a grid-like effect on the image, however, given the prospects for introducing resolutions exceeding Full HD while maintaining the screen diagonal size, this issue will disappear in the near future. Another serious drawback inherent in LCD projectors, is a fairly high black level, and, as a result, low contrast, but in fairness it is worth noting that modern solutions based on IPS matrices are already demonstrating very impressive results. In addition, the insufficient performance of LCD panels has also long ceased to stand in the way of high-quality images. But noise is still a pressing drawback. The point is that in these projectors Powerful gas-discharge lamps are used, which require a serious cooling system that uses fans, which leads to increased noise levels. It is also worth noting that the lamp life is from 2000 to 4000 hours, after which the brightness decreases by half, which means that with intensive use it will have to be changed periodically, which is associated with significant financial investments. In addition, the matrices themselves also tend to change their properties over time.

By the way, that very first and simple version of projection technology, when one LCD panel and a light source are used, served as the basis for many home-made designs. There are still many instructions on the Internet on how to make a projection device yourself using a monitor matrix and projector for lectures.

LCoS (Liquid Crystal Reflective Technology)

The closest relative of the 3LCD imaging principle is LCoS technology, which stands for Liquid Crystal on Silicon. So what's the point? To put it quite simply, the light flux is modulated by a liquid crystal matrix, which works not for transmission, but for reflection. How is this implemented in practice? On the substrate there is a control semiconductor layer covered with a reflective surface, and above this “sandwich” there is a matrix of cells with liquid crystals, protective glass and a polarizer. Light from the source hits the polarizer, is polarized and passes through the liquid crystal cell. A signal is applied to the semiconductor layer, which allows you to control the plane of polarization of the incoming light by changing the spatial orientation of the liquid crystal. In this way, the cell becomes more or less transparent, allowing you to control the amount of light that passes to and from the reflective layer.

Several commercial technologies have been developed based on this imaging principle, all of which have been patented. Some of the most famous are SXRD from Sony and D-ILA from JVC. By the way, it is worth noting that despite the fact that both of them are actively used to this day, the starting point should be considered the distant 1972, when the liquid crystal optical modulator was invented. The military became interested in the technology, and a few years later all command centers of the US Navy were equipped with these devices. Of course, these were completely analog devices and, by the way, cathode ray tubes acted as the image source in them. Needless to say, they were prohibitively complex and expensive. Already in our time, the commercial development and improvement of the principle of modulation of reflected light was undertaken by the JVC company, which introduced the first one based on D-ILA technology in 1998. So, how does such a device work?

Currently, solutions based on three matrices are mainly used, but in fairness it is worth saying that single-chip LCoS- ones also exist. Two schemes are usually used. In the first case, the light source is three powerful LEDs of red, green and blue colors, which switch sequentially and with high speed, and frames are synchronously formed on the reflective matrix for each stream. In the second case, the white light from the lamp is divided into components directly on the matrix using a special filter, and the array of cells itself forms a full-color image. These are not widely used either because of the low luminous flux or because of the complexity of production. Therefore, as in the case of translucent liquid crystal panels, the most successful scheme was with three LCoS matrices.

So, the light from the source is divided into three light streams, corresponding to red, green and blue, using a system of dichroic and simple mirrors. Next, each of them falls on its own polarizing prism (PBS). The streams are then directed to the reflective matrices, modulated to form color components for the base image channels, passed back through the PBS elements and brought together in a dichroic prism. The resulting image is projected through the lens onto the screen.

D-ILA technology diagram

The advantages of this technology can be confidently called excellent image quality, high brightness and contrast of the image, as well as the ability to project images in very large formats. It is also worth noting that the manufacturing features of reflective matrices make it possible to place control conductors and electronics behind the reflective layer, which means that the pixel coverage area is much larger. In other words, the image looks much more uniform than with translucent panels. In addition, JVC's point array control is implemented using analog signals, which allows for smoother gradients. And the production technology, among other things, makes it possible to create matrices with very high resolution, which will certainly be very relevant in the light of the introduction of 4K image standards.

As for the disadvantages, first of all it is worth mentioning the very high price. Only very wealthy home theater enthusiasts can afford this. In addition, such devices cannot be called compact and lightweight, so they are unlikely to be used in mobile presentations. Their destiny is large and medium-sized cinema halls. Since these devices use the same gas-discharge lamps as translucent liquid crystal lamps, all the disadvantages associated with their use are fully present here. Let us remember that this is, first of all, the noise of active cooling systems, as well as the limited service life of the lamp, the replacement of which will cost a significant amount.

DLP (micromirror technology)

The third, and most active player in the market of modern projection devices, can confidently be called DPL technology, which also works on the reflective principle. Its name is an abbreviation for Digital Light Processing, which can be translated as " Digital Processing Light." This technology is based on a special microelectromechanical system, which is a tiny mirror, the position of which is controlled by equally miniature mechanics, controlled by electrical signals. The mirror can be in two positions. In the first case, it reflects light, which, after passing through the entire path, forms a point on the screen. In the second position, the light hits a special light-absorbing device. It is worth noting that due to its very small size, the mirror can switch between two states very quickly. Since the principle of operation and control is similar to binary (no light - logical zero, light present - logical one), devices of this type are considered digital.

In order to form an image, you will need whole array such micromirrors along with control mechanics, so engineers developed a special microchip made using microelectronic technology, which is called DMD or Digital Micro Device - “Digital Micro Device”.

It is worth noting that this technology was developed by Texas Instruments back in 1987, and to this day DMD matrices are produced only by this company. By the way, the first commercial sample of a DLP-based projection device was presented only in 1996. So how do these things work?

There are two main schemes on the market: single-chip and three-chip. The first is cheaper and, accordingly, more popular, and the second is more expensive and less common.

So, the circuit with one DMD chip works as follows. Light from the source passes through a rapidly rotating transparent wheel, which is divided into several colored segments. To a first approximation, these are red, green and blue colors. Next, the colored light beam is projected onto the DMD chip, strictly synchronized with the disk on which the micromirrors have already formed a frame for a given color. The reflected flow is projected through the lens onto the screen. Since, as already mentioned, only one of two positions is possible for each micromirror, the shades of colors are formed during the light of the time that each micromirror spends in a state of reflection. And everything else is done by our consciousness and the inertia of vision, so on the screen we see not individual colors, but a smoothly changing image.

Single-chip DLP technology diagram

The main advantages of this scheme today are high brightness and excellent image contrast. Due to the design of DMD chips, DLP devices also feature unprecedented response times. Since the principle of reflection works here, the efficiency of using the luminous flux in such lamps is very high, which means that lamps of lower power are required to obtain the required brightness values. This reduces energy consumption as well as noise active system cooling. It is also worth noting that DMD chips retain their original characteristics over time. In addition, due to the simplicity of the design, such devices, as a rule, are characterized by a relatively low price and compact dimensions. In terms of image uniformity and pixel visibility on the screen, DLP technology is right between 3LCD and LCoS.

As for the shortcomings, they are also quite significant. In the first models, the color wheel rotated at a speed of up to 3600 revolutions per minute, so the speed of displaying individual images on the screen, on the one hand, was very high, but on the other, still insufficient. Because of this, the viewer could periodically observe the so-called “rainbow effect.” Its essence is that if a bright object was displayed on a dark background on the screen, and the gaze was quickly moved from one edge of the frame to the other, then this bright object would disintegrate into red, blue and green “phantoms”. Moreover, there were enough such scenes in the films, and the discomfort from watching them was also noticeable.

To reduce its influence, developers began to spin the color wheel and increase the number of segments on the disk. At first there were the same red, green and blue segments, but there were six of them, and they were already located opposite each other. Thus, the output frame rate doubled, and the “rainbow effect” became less noticeable. There were options with the addition of segments of intermediate colors, but the result was almost the same - less noticeable, but still present. By the way, it is worth mentioning separately the problem of color and brightness in DLP-. The three-segment wheel made it possible to obtain good color rendition, but still reduced brightness, so they began to add an uncolored section to it. This made it possible to increase the luminous flux, but led to bleached colors with a small number of gradations. Then Texas Instruments created Brilliant Color technology (with the same six-segment disk with additional intermediate colors), which helped correct the situation. Currently, there are models on the market with the number of individual segments on the color wheel reaching seven.

To be fair, there are also dual-chip DLPs that also use a color wheel to separate light into two components, which are mixtures of red and green and red and blue. Using a system of prisms, the red component is isolated, which is directed to one of the micromirror arrays. The green and blue components are alternately projected onto the other chip. Next, two DMD matrices modulate the corresponding beams, so that a red frame is constantly projected onto the screen, which makes it possible to compensate for the insufficient intensity of the corresponding part of the lamp’s emission spectrum. It is worth noting that with the increase in cost (due to the use of two micromirror chips), such a scheme did not completely solve the problem of the “rainbow effect”, and was not widely used. Therefore, manufacturers had no choice but to use a design with three micromirror chips.

In three-matrix systems, the light flux from the light source is divided into three components using an array of special prisms. Each beam is then directed to the corresponding micromirror panel, modulated and returned to the prism, where it is combined with other color components. Next, the finished full-color image is projected onto the screen.

Three-chip DLP technology diagram

The advantages of such a scheme are obvious: high brightness and contrast, low response time, absence of the “rainbow effect”, which means comfortable viewing. Again, the high efficiency of using the luminous flux in these allows the use of lower power lamps, which, in turn, reduces energy consumption and noise of the active cooling system.

The main disadvantage is also quite obvious: the price. The cost of one DMD chip separately is very high, and even more so of three, so three-matrix models mainly serve the middle segment of home theaters. The second difficulty is that, due to the design of the optical path in DLP, it is extremely difficult to perform a mechanical lens shift, so it can only be found in expensive models.

Returning to the single-chip circuit, it is worth noting that the modern development of optical semiconductor technologies and the emergence of LEDs and lasers in blue and green colors have made it possible to develop models that do not have the “rainbow effect”. The most simple option was the replacement of the gas-discharge lamp with three powerful LEDs of primary colors. Light sources can turn on and off very quickly, so this scheme also made it possible to abandon the color wheel, as well as further increase the speed of changing color frames. In addition, it was possible to greatly reduce the energy consumption and dimensions of the device, including due to a simpler cooling system. And less heat generation also has a positive effect on the operation of all electronics. The first one appeared in 2005 and weighed less than half a kilogram, while its luminous flux was sufficient to project an image with a diagonal of 60 inches.

DLP LED technology diagram

The next step was the use of semiconductor lasers as a light source. The fact is that the use of such sources is considered very promising, due to their excellent color, time and energy characteristics. In addition, the light emitted by lasers also has circular polarization, which can be quite simply converted to linear and thus simplify the design. So, sources of coherent radiation with wavelengths corresponding to red, green and blue colors are alternately supplied to special diffraction shapers, which ensure uniformity of light across the entire cross section of the beam. Then, after being aligned by a system of dichroic mirrors, each color component passes through an optical converter, which turns the thin beam into a wide beam of light. An array of micromirrors modulates the incident light, and the resulting image of the appropriate color is projected onto the screen.

DLP laser technology diagram

The most significant improvement in such schemes is the absence of the rainbow effect, as well as remarkable results in color rendering, brightness and contrast. The use of semiconductor LEDs and lasers as a light source has made it possible not only to significantly reduce energy consumption, but also to significantly increase the resource. Manufacturers claim a mean time between failures of 10,000 to 20,000 hours. In addition, the brightness of the source remains constant throughout its operation. True, such devices are not yet available to everyone: the price of an innovative product is still at a very high level.

Let us add that on the market you can find models that use both lasers and LEDs as a light source. To be very precise, there is only one laser - blue, which, however, is responsible for the green component. How is this possible? The fact is that a blue laser shines on a special plate coated with a phosphor, which begins to glow green. The red and blue components of the image are formed by the corresponding LEDs. Well, then everything is as usual: light with different wavelengths hits the DMD chip one by one, and then is displayed on the screen.

In addition, this scheme has variations with a color wheel, but not a translucent one, but coated with a phosphor. In the first case, red light is generated by an LED, and green and blue are generated by a blue laser, which is directed at a rotating disk with two types of phosphor, which alternately glow with blue and green light. In the second version, there is no red LED, and all three colors are formed by a laser and a color wheel with three different phosphors. The fact is that the phosphor allows you to avoid the so-called spotty noise, and the use of a laser allows you to achieve very rich shades.

LDT (laser technology)

In the previous sections, we looked at the currently most popular technologies that are widely represented on the market. Now it’s time to get acquainted with a very exotic method of image formation.

In the chapter on DLP, we looked at the use of semiconductor lasers as a light source. What if the laser beams themselves form an image directly on the screen? This question has been worrying humanity for decades, but the answer to it was received in 1991, after LDT or Laser Display Technology was invented, which translates as “Laser Display Technology”. A working prototype was presented in 1997, and a production prototype in 1999. So, what is remarkable about the physical principle based on the use of lasers?

Before answering this question, it is worth understanding why such technology was needed to be developed in the first place. The fact is that the projection devices of the 90s of the last century were not good enough to reproduce very bright and at the same time very contrasting images with high resolution. Lasers, due to their physical characteristics, could correct the situation.

It is worth noting that attempts to use coherent light sources to form images have been made quite a long time ago, since the 60s. Moreover, the original idea was to replace cathode ray tube beam of electrons onto a laser beam. In this case, the design was significantly simplified, and color rendition was improved. However, at that time it turned out to be impossible to overcome some technical difficulties, such as creating lasers that operate at room temperature, as well as beam deflection systems. By the way, similar work was carried out in the USSR. The development of semiconductor and microelectronic technologies has made it possible to overcome the above difficulties and create LDT-, however, the mass introduction of such devices is still very far away.

So how does LDT technology work? The system is built on using three lasers of basic colors, which are modulated in amplitude by special electro-optical devices. Using a special system of translucent mirrors, the rays are combined into one light stream, which is not yet a full-fledged color image. Next, the signal is sent via an optical cable to an optical-mechanical image scanning system. The frame is built according to the same principle as on TV - line by line: from left to right and from top to bottom. The image is scanned along one axis using a special rotating drum with twenty-five special mirrors, and along the other - by deflecting the beam with a swinging reflector. It is worth noting that the laser is capable of describing 48,000 lines or 50 frames per second on the screen, and the speed of moving a point on the screen reaches 90 km/s! This speed is, of course, very high for our rather inertial perception, which allows us to see a smoothly changing image on the screen. After scanning, the light signal enters the focusing system, which is combined with deflection devices into the projection head. By the way, one of the features of the system is that the light source can be removed from the projection device at a distance of about 30 meters, which, in turn, means the possibility of using very powerful lasers that require special systems cooling, and, therefore, obtaining an image of enormous brightness.

LDT laser technology diagram

What advantages does this principle of projection formation have? Firstly, as already mentioned, this is the enormous brightness of the image, and, as a result, the ability to project an image over an area of ​​​​several hundred square meters. In addition, it can be projected not just onto a plane, but onto anything in general - and the image will remain sharp at every point! And all thanks to lasers: they allow you to get rid of the complex system of mixing and focusing beams. Moreover, all other advantages are also due to the physical nature of coherent radiation. For example, lasers scatter very weakly, so generated image has a very high contrast, four times greater than human vision! In addition, since lasers are highly monochromatic, the picture also has an expanded color gamut and high saturation. In addition, the operating time of radiation sources is tens of thousands of hours, so no traditional gas-discharge lamps are able to fully compete with them. The same can be said about energy consumption.

LDT technology is still very young and has some drawbacks. For example, the same color rendition. To color each beam, special crystals are used that change the wavelength, so achieving an exact match is not at all easy. The developers are working on this issue, but for now it is quite relevant. The dimensions of the device are not small at all, so only a special team can handle its mobility. Well, perhaps the main drawback of the technology is the huge price, which in principle is not surprising, since this product is still very far from becoming a mass product. Therefore, at present, LDT technology may only be of interest to large companies that specialize in concert activities, large light shows, and installations for serious conferences.

Projector device | Technologies for forming three-dimensional images

Humanity has been interested in projecting three-dimensional images almost since the invention of cinema. Many implementation options were proposed, but the basic principle always remained the same: for each eye, its own image should be generated.

Modern interest in three-dimensional images arose after the release of James Cameron's film Avatar in 2009. The world of the planet Pandora, shown in the film in stereoscopic format, was so realistic that a new wave of fashion for three-dimensional images was not long in coming. By that time, it was already an integral part of a full-fledged home theater, so equipment manufacturers tried to introduce the new technology as quickly as possible not only into televisions, but also into projection devices.

Unfortunately, the developers were unable to agree on a single format, so at the moment two main technologies dominate the market: polarization and shutter. The first is based on image separation using polarizers. The first commercial implementation of this idea used linear polarization, with the planes of wave direction for each eye being mutually perpendicular. In practice, everything was implemented as follows. Using two, two images are projected onto the screen, polarized for each eye, special glasses separate the images, and the viewer perceives objects on the screen as three-dimensional. This method of formation had several disadvantages: the need to use two, as well as a special screen that had increased reflectivity and did not change the direction of polarization. In addition, the viewer always had to keep his head straight so that the three-dimensional effect would not disappear. The next step in the development of this technology was to replace linear polarization with circular polarization, and project frames for each eye alternately using only one device. This approach made it possible to hold the head freely while viewing, but led to the loss of half the light flux. Polarization technology, for all its advantages, is practically not used in home theaters, but is used mainly in the professional field.

The second option for obtaining a three-dimensional image is based on dividing frames for each eye using special glasses. displays alternate images for each eye, and the frame rate can reach 120 Hz. Instead of lenses, active glasses use special LCD matrices that are synchronized with and block the light flux in such a way that each eye sees only the images intended for it. Since, as we have already said, our perception is quite inertial, the flows are perceived continuously and put together into a single three-dimensional picture. It is this technology that is currently most actively used in home theaters, although in fairness it is worth noting that it is also quite popular in the professional environment.

So, the process of obtaining a three-dimensional image is clear, it remains to figure out which ones allow you to reproduce such a picture. At the present stage of development of projection technologies, obtaining a three-dimensional image has been achieved on the basis of LCD, DLP and LCoS systems. True, given that the shutter method has been used in home theaters quite recently, the developers still have many issues to resolve. For example, the performance of LCD matrices does not yet fully meet the requirements for update speed and response.

Projector device | Conclusions and prospects

So, we got acquainted with the main projection technologies for forming images in a cinema format, and also examined their features, advantages and disadvantages. Just ten years ago, they were very exotic display devices that were just beginning a massive offensive in the field of home use. Over the years, image quality has reached a very high level, many of the technological shortcomings of early models have been overcome, and the variety of devices allows you to choose one to suit your taste at a very reasonable price. Even the sudden fashion for three-dimensional images was immediately reflected in the produced models.

Today the situation looks like this. The most common technology can confidently be considered DLP. , built on micromirror panels, are found both in the low-cost and mid-range segments. In addition, this technology is also very promising, for several reasons. Firstly, the introduction of LED and laser light sources will help create mass projection devices that will be very miniature and low-power, with high luminous flux, excellent contrast, remarkable color gamut and long service life. And, secondly, the high performance of such panels creates excellent opportunities for the implementation of high-speed methods for forming three-dimensional images.

The closest competitor to DLP is 3LCD technology. Despite the fact that this scheme is not new, it is still very popular in both inexpensive and mid-priced devices. Moreover, despite the inherent limitations, for example, in contrast and in the size of the distance between pixels, each new generation of matrices never ceases to amaze with excellent results. So today, the technological limit of the capabilities of this imaging method has not yet been reached.

Liquid crystal technology on silicon today is one of the highest quality in terms of picture parameters, however, it is also one of the most expensive, so these are used only in top-level home theaters. Nevertheless, such models become more accessible every year and even appear in the middle price segment, but in this respect they are still very far from DLP and LCD.

The question of the possible impact of the projected image on human health arises from time to time. It is believed that the image generated using 3LCD and LCoS technologies does not have any negative aspects, since it is transmitted to the screen in a flattened form, while DLP with one micromirror chip sequentially forms three multi-colored images at high speed. By the way, some studies show that a frame rate of 180 Hz is not enough to completely eliminate the “rainbow effect” and associated visual fatigue during prolonged viewing.

As for the prospects for the development of projection technology, very high hopes are associated with the introduction of semiconductor light sources, such as LEDs and lasers, not only in the field of home cinema, but also in the field of professional equipment for concerts and light shows. We have already talked about the advantages that this technology provides, so it’s worth saying a few words about the possible consequences. So far, the method of forming images using laser beams is not only very promising, but also very young, which means there is practically no data on the possible impact on human health. However, it has long been known that a laser beam with a radiation power of 1 mW can be dangerous to vision, and, therefore, when using such a technique, the possibility of direct light beam hitting the audience should be completely excluded. In general, the safety issue remains to be investigated.

Perhaps in the near future, all the efforts of projection equipment manufacturers may be in vain, since, paradoxically, OLED technology may become the main competitor in the home theater market. Judge for yourself: today you won’t surprise anyone with LCD TVs with a diagonal of 1.5 meters, and record-breaking models even show a picture of more than 2.7 meters, despite the fact that the average image size in a home theater is exactly about 3-4 meters diagonally. There are already commercial samples of OLED TV models based on flexible substrates, which make it possible to produce not only flat, but even concave screens. And this, in turn, paints very tempting prospects for us: perhaps in the future we will no longer need either screens or screens. In order to immerse yourself in the action of the film, all you have to do is press the electric drive button and a huge flexible canvas covered with organic LEDs will smoothly appear from the wall niche. All that remains is to turn on the movie and enjoy the image.

In the era of high-definition technology, projectors are becoming increasingly popular because they allow you to recreate the atmosphere of a real cinema at home. Of course, this idea can also be implemented using an LCD TV with a large screen diagonal and support for the 4K video standard.

However, content with such a resolution is still rare, and TVs in this class are not cheap. Modern Full HD projectors are capable of providing excellent image quality, and they also take up significantly less space.

LCD vs DLP

Modern projectors use LCD (Liquid Crystal Display) and DLP (Digital Light Processing) technologies, which differ in the principle of image formation. In the case of DLP, the role of a pixel is played by a miniature mirror. In front of a set of such “pixels” there is a rotating filter, divided into colored segments.

Light is transmitted through a filter, hits the mirrors and is reflected from them onto the screen. LCD technology uses matrices that are illuminated by light reflected from a system of mirrors. Each mirror is a light filter and supplies only one of the three primary colors to the matrix.

Of course, both of these technologies have both advantages and disadvantages: for example, LCD projectors provide rich colors, while DLP solutions have higher contrast. Among the disadvantages of LCD models, it is worth noting the lower depth of black color, and DLP projectors have a “rainbow effect”. However, in modern devices these shortcomings are almost invisible.

According to the results of our various comparative tests, LCD projectors, although not by much, are still ahead of DLP solutions in picture quality. As you know, LCD projection technology was developed by the Japanese company Epson, and the first device based on this principle was created 25 years ago. All these years the technology has been significantly improved and refined.

A 3D projector from Epson worth 75,000 rubles supports Full HD resolution, allows you to connect smartphones and tablets via the HDMI MHL connector and is capable of displaying an image with a diagonal of up to 300″