Projector device description. Coursework: Multimedia Projector. Best Multimedia Projector

The device of projectors | Introduction

All of us are fascinated by the magical world of cinema. The atmosphere of the cinema allows you to fully immerse yourself in the action and feel the director's intention, feel a surge of emotions and even, to some extent, live the life of screen heroes. Of course, hardly anyone would argue that one of the main aspects of such a strong impact is a bright, rich, large format image. And today such a picture can be obtained only with the help of projector- a device that uses a light source to project frames onto a screen. It should be noted 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 in a rather simplified way, then the first spectators can be considered primitive people who observed moving shadows from the fire on the vaults of caves. Then the famous Chinese shadow theater comes to mind, using what we might call back-projection today. And the first mass devices appeared only in the 17th century. They were called "magic lanterns", the inventor of which is believed to be the Dutch scientist Christian Huygens. The design of the 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 the optical system located in the front of the device and hit the screen.

The history of the magic lantern goes back almost three centuries, and all this time the design was improved. For example, to enhance the luminous flux, a reflector was added a little later, and in the 19th century, the candle was replaced by an electric lamp. By the way, wandering artists often used magic lanterns, surprising the audience with an unprecedented light show. It should be noted that such devices were also common in pre-revolutionary Russia, where they were used for educational purposes. Moreover, the overhead projector, loved by us since childhood, is a direct heir to the magic lantern. Also, one cannot fail to mention the defining 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 caused a rapid progress in equipment not only for filming, but also for reproduction, which continues to this day. There are specialized training devices such as overhead projectors that 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, which means they could be used to show films outside cinemas. Further development of technologies made it possible to organize viewing, in no way inferior to theatrical, at home. The idea of ​​a home theater has captivated movie enthusiasts and lovers alike and sparked a new surge of interest in the film production industry. In addition, the massive demand for projectors became the reason for a significant reduction in the cost of technology and the development of truly affordable models. And this, in turn, made it possible to widely use projection equipment in other areas, such as education.

So, all modern methods of forming projection images can be divided into three groups: emitting, 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 in the market.

The device of projectors | 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 progenitors of home theaters, since they made it possible to form huge images even before no one had heard of liquid crystals or micromirrors. So what is CRT- projector?

The principle of operation 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 are accelerated by high voltages. Then the electromagnetic deflection system focuses the beam and changes the direction of movement of the charged particles, as a result of which they bombard the inner surface of the glass screen, covered with a phosphor, which begins to glow under the influence of electrons. Thus, the electron beam, tracing each frame line by line, and forms a picture on the screen. However, since monochrome vacuum elements are used in such devices, one CRT is not enough to obtain a full color image. Therefore, in CRT- projectors three tubes are installed, which are responsible for the formation of the basic colors: red, green and blue. By the way, since such devices always require a large luminous flux, the screen diagonal of each CRT can be up to 9 inches. Then all three images are combined on the screen using massive lenses and various analog distortion correction systems.

CRT technology diagram

As for the image quality, even today it can be called remarkable. Firstly, it has excellent color rendition. Secondly, the ability to reproduce low black levels, and, as a result, to display a picture with high contrast. And, thirdly, the ability to reproduce almost any input signal resolution. Moreover, such projectors can change the geometry of the picture, leaving the number of picture elements constant. True, it should be noted 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 yet they can continuously work for hundreds of hours, although, again, such an advantage is practically not required for a regular home theater. It is also worth noting that such an image projection technology has been more than tested by time, because its history goes back about fifty years, which means that all possible difficulties of production and operation have long been overcome. By the way, such devices are still being produced.

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

Considering that modern technologies reproduction of large-format images, driven by the fashion for a three-dimensional picture and the introduction of ultra-high-definition standards, are developing at a tremendous speed, CRT- projectors against the background of current models, they look like a kind of dinosaurs: the same 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 should be noted that the formula "new is 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 the movie projector with an LCD matrix showing the video sequence. 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 large format picture reproduction tools and, as a result, a whole direction of mass home theaters.

So how does LCD work projector? The functioning is based on the property of molecules of a liquid crystal 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 the picture? Everything is 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 element of the image. Of course, such a representation of the principle of operation is rather simplified, but once everything worked this way. Now add control transistors, wires, additional pixels for each color channel, corresponding color filters - and you get a color LCD 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 this is not yet projector: we need a powerful lamp, a cooling system, control electronics, a power supply, a lens for projecting an image and a housing. At first glance, everything is quite simple, but the use of one matrix almost immediately revealed several serious drawbacks: 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 three-matrix circuit, which was named 3LCD.

This constructive solution turned out to be so popular that it is used in projectors still. What is its peculiarity? The fact that, as you might guess from the name, three matrices are involved in the formation of the image at once. So, light from a source (usually a gas-discharge lamp) hits a system of dichroic mirrors, which are installed in the optical unit. Their task is to transmit light of a certain spectrum and reflect everything else. Thus, white light is split into three streams that form the basic colors of the image: red, green, and blue. Each ray 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 converging the three images. In addition, the introduction of polysilicon technology has 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 an additional increase in their resolution has appeared. In modern projectors microlens raster panels are also used, which direct the light flux through transparent area and thus give an additional gain in brightness. It should be noted that the technological process continues to improve until now, since the limit of possibilities has not yet been reached.

So, the main advantages of the image formation technology based on three LCD matrices are high brightness of the picture, 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 a large distance between pixels, which is a consequence of the need to place conductors and control transistors between the cells. This leads to the effect of a gridded image, however, given the prospects of introducing resolutions exceeding Full HD while maintaining the screen diagonal, this issue will disappear in the near future. Another serious flaw inherent in LCD projectors, is pretty high level black, and, as a result, low contrast, but in fairness it should be noted that modern solutions based on IPS-matrices are already demonstrating very impressive results. In addition, the lack of performance of LCD panels has long been no longer standing in the way of high-quality images. But noise is still a real drawback. The fact is that in these projectors high-power discharge lamps are used, requiring a serious cooling system, which uses fans, which leads to an increased level of noise. 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 you will have to periodically change it, which is associated with significant financial investments. In addition, the matrices themselves also tend to change their properties over time.

By the way, the very first and simple version of projection technology, when one LCD panel and a light source are used, served as the basis for many homemade designs. There are still many instructions on the Internet for self-production a projection device 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? Quite simply, the luminous 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 are a matrix of cells with liquid crystals, a protective glass and a polarizer. Light from the source hits the polarizer, polarizes 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. Thus, the cell becomes more or less transparent, allowing you to control the amount of light that passes to the reflective layer and back.

Several commercial technologies have been developed based on this principle of imaging, and each of them has been patented. Some of the most famous are Sony's SXRD and JVC's D-ILA. 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 the 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 an image source in them. Needless to say, those were prohibitively difficult and expensive. Already in our time, the commercial development and improvement of the principle of reflected light modulation was taken up by JVC, 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 should be said that there are also single-chip LCoS-. Two schemes are commonly used. In the first case, the light source is three powerful red, green and blue LEDs, which are switched sequentially and at high speed, and frames for each stream are synchronously formed on the reflective matrix. 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. Such ones have not become widespread either because of the low luminous flux, or because of the complexity of production. Therefore, as in the case of transmissive liquid crystal panels, the scheme with three LCoS matrices has become the most successful.

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

D-ILA technology diagram

The advantages of this technology can be confidently called the remarkable image quality, high brightness and contrast of the picture, as well as the ability to project images of very large formats. It is also worth noting that the peculiarities of the production of reflective matrices allow placing control wires 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 in the case of transmissive panels. In addition, JVC's point array control is implemented using analog signals, resulting in smoother gradients. And the production technology, among other things, allows you to create matrices with very high resolution, which, of course, will be very relevant in the light of the introduction of 4K image standards.

As for the shortcomings, 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 lot is large and medium-sized halls of cinemas. Since these devices use the same gas-discharge lamps as in transmissive liquid crystal lamps, all the disadvantages associated with their use are fully present here. Recall that this is, first of all, the noise of active cooling systems, as well as the limited life of the lamp, the replacement of which will cost a significant amount.

DLP (micromirror technology)

The third and most active player on the market of modern projection devices is DPL technology, which also works on the reflective principle. Its name is an abbreviation for Digital Light Processing, which can be translated as "Digital Light Processing". This technology is based on a special microelectromechanical system, which is a tiny mirror, whose position is controlled by an equally miniature mechanic, 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 the two states very quickly. Since the principle of operation and control is similar to binary (no light - logical zero, light is - logical unit), devices of this type are considered digital.

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

It should be noted 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 prototype of a projection device based on DLP 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, a circuit with one DMD chip works as follows. The light from the source passes through a rapidly rotating transparent wheel, which is divided into several colored segments. As a first approximation, these are red, green and blue. Then 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 the given color. The reflected stream 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 the rest 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 such a scheme today are high brightness and excellent image contrast. Thanks to the design of the DMD chips, DLP devices also have unprecedented response times. Since the principle of reflection works here, the efficiency of using the luminous flux in such is very high, which means that lower power lamps are required to obtain the required brightness values. This reduces energy consumption as well as noise from an active cooling system. It is also worth noting that DMD chips retain their original characteristics over time. In addition, due to the simplicity of their design, such devices, as a rule, are distinguished by a relatively low price and compact dimensions. In terms of image uniformity and pixel visibility on the screen, DLP technology is just 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 rpm, so the speed of displaying individual images on the screen, on the one hand, was very high, and on the other, it was still insufficient. Because of this, the viewer could periodically observe the so-called "rainbow effect". Its essence lies in the fact that if a bright object was displayed on the screen against a dark background, and the gaze was quickly moved from one edge of the frame to the other, then this bright object disintegrated into red, blue and green "phantoms". Moreover, in films there were enough such scenes, and the discomfort from watching was also noticeable.

To reduce its influence, the developers began to spin the color wheel and increase the number of segments on the disk. At first there were all the same red, green and blue segments, but there were six of them, and they were already located opposite each other. This doubled the frame rate and made the "rainbow effect" 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, the problem of color and brightness in DLP is worth mentioning separately. The three-segment wheel made it possible to obtain good color rendering, but still reduced the brightness, so they began to add an uncolored area to it. This allowed for increased luminous flux, but resulted in whitewashed colors with few gradations. Then Texas Instruments created Brilliant Color technology (thus a six-segment disc with additional intermediate colors), which helped to fix the situation. Currently, there are models on the market with the number of individual segments on the color wheel reaching seven.

For the sake of fairness, it should be said that there are also two-chip DLP-, which also use a color wheel to separate light into two components, which are mixtures of red with green and red with blue. With the help of a system of prisms, the red component is selected, which is directed to one of the micromirror arrays. The green and blue components are alternately projected onto another chip. Further, two DMD-matrices modulate the corresponding beams, thus the 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 radiation spectrum. It should be noted that with an 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 did not become widespread. Therefore, manufacturers had no choice but to use a design with three micromirror chips.

In three matrixes, the luminous flux from the light source is divided into three components using an array of special prisms. Then each beam is 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, no "rainbow effect", which means viewing comfort. Again, the high efficiency of using the luminous flux in such allows the use of lamps of lower power, which, in turn, reduces the power consumption and noise of the active cooling system.

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

Returning to the single-chip scheme, it is worth noting that the modern development of optical semiconductor technologies and the emergence of blue and green LEDs and lasers have made it possible to develop models in which the "rainbow effect" is absent. The simplest option was to replace the gas-discharge lamp with three powerful LEDs in primary colors. Light sources can be turned 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 power 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 such 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 circuit

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 the excellent color, time and energy characteristics. In addition, the light emitted by lasers is also circularly polarized, which can be easily converted to linear polarization and thus simplify the design. So, sources of coherent radiation with wavelengths corresponding to red, green and blue are alternately supplied to special diffraction shapers, which ensure the uniformity of light over the entire cross section of the beam. Then, after alignment with a system of dichroic mirrors, each color component passes through an optical converter, which converts a thin beam into a wide luminous flux. An array of micromirrors modulates the incident light, and the resulting image of the corresponding color is projected onto the screen.

DLP laser technology diagram

The most significant improvement in these schemes is the lack of rainbow effect, as well as remarkable results in color rendering, brightness and contrast. The use of semiconductor light-emitting diodes and lasers as a light source allowed not only to significantly reduce power consumption, but also to significantly increase the resource. Manufacturers claim MTBFs between 10,000 and 20,000 hours. In addition, the brightness of the source remains constant throughout the entire operating time. True, such devices are not yet available to everyone: the price of an innovative product is still at a very high level.

We add that on the market you can find models that use both lasers and LEDs as a light source. To be absolutely precise, there is only one laser - blue, which, however, is responsible for the green component. How is this possible? The fact is that the blue laser shines on a special plate covered with a phosphor, which starts to glow with green light. 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, the red color is formed by an LED, and the green and blue ones are formed by a blue laser, which is directed at a rotating disk with two types of phosphor, which alternately glow blue and green. In the second version, the red LED is absent, 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 - to achieve very saturated shades.

LDT (laser technology)

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

In the DLP chapter, we looked at the use of semiconductor lasers as a light source. But what if the laser beams themselves form an image directly on the screen? This question has worried mankind for more than a decade, but the answer to it was received in 1991, after the LDT or Laser Display Technology was invented, which translates as "Laser Display Technology". A working prototype was presented in 1997, and a serial one in 1999. So, what is so remarkable about the physical principle based on the use of lasers?

Before answering this question, it is worth understanding why it was necessary to develop such a technology at all. 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 should be noted that attempts to use coherent light sources for image formation have been undertaken for a long time, since the 60s. Moreover, the original idea was to replace the electron beam in the cathode-ray tube with a laser beam. In this case, the design was greatly simplified and the color rendition improved. However, at that time, it turned out to be impossible to overcome some technical difficulties, such as the development of lasers operating 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 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 based on the use of three lasers of basic colors, which are amplitude modulated by special electro-optical devices. With the help of a special system of translucent mirrors, the rays are combined into one luminous flux, which is not yet a full-fledged color picture. Then the signal is fed via an optical cable to the optical-mechanical image scanning system. The frame is built according to the same principle as on the 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 48000 lines or 50 frames per second on the screen, and the speed of the point moving 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 goes to the focusing system, which is combined with deflectors in 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 requiring special cooling systems, and, therefore, obtaining an image of a huge brightness.

Diagram of LDT laser technology

What are the advantages of this principle of projection formation? Firstly, as already mentioned, this is the enormous brightness of the image, and, as a result, the ability to project a picture with an area of ​​several hundred square meters... In addition, it can be projected not just on a plane, but in general on anything you like - 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 converging and focusing beams. Moreover, all other benefits are also due to the physical nature of coherent radiation. For example, lasers are very weakly scattered, so the created image has a very high contrast, four times the capabilities of human vision! In addition, since lasers are highly monochromatic, the picture also has an extended 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 can fully compete with them. The same can be said for power consumption.

LDT technology is still very young and has some disadvantages. For example, all the same color rendition. To color each beam, special crystals are used that change the wavelength, so it is not at all easy to achieve an exact match. The developers are dealing with this issue, but so far it is quite relevant. The dimensions of the device are not at all small, so the mobility of such a device is only possible for a special team. Well, and, 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 being a mass product. Therefore, at present, LDT technology can only be of interest to large companies that specialize in concert activities, large light shows, as well as installations for serious conferences.

The device of projectors | 3D imaging technologies

Humanity has been interested in projecting a three-dimensional picture almost since the invention of cinematography. There were many options for implementation, but basic principle has always remained unchanged: for each eye its own image must be formed.

The modern interest in three-dimensional painting arose after the release of James Cameron's film "Avatar" in 2009. The world of the planet Pandora, shown in the picture in a stereoscopic format, was so realistic that a new wave of fashion for a three-dimensional image 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 implement the new technology as quickly as possible, not only in televisions, but also in projection devices.

Unfortunately, the developers were unable to agree on a unified format, so at the moment the market is dominated by two main technologies: polarizing and shutter. The first is based on the separation of pictures using polarizers. Initially, the commercial implementation of this idea used linear polarization, with the plane of direction of the waves for each eye were mutually perpendicular. In practice, everything was implemented as follows. With the help of two, two images are projected onto the screen, polarized for each eye, special glasses separate the pictures, and the viewer perceives objects on the screen as three-dimensional. There were several disadvantages of this method of formation: the need to use two, as well as a special screen, which had an 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 the replacement of linear polarization with circular polarization, as well as projecting frames for each eye alternately using only one device. This approach made it possible to hold the head arbitrarily while viewing, however, it led to the loss of half of the luminous flux. Polarization technology, with all its advantages, is practically not used in home theaters, but is mainly used in the professional field.

The second option for obtaining a three-dimensional image is based on the division of frames for each eye using special glasses. shows alternately images for each eye, while the frame rate can be up to 120 Hz. Instead of lenses in active glasses, special LCD matrices are used, which 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 streams are perceived continuously and add up to a single three-dimensional picture. It is this technology that is currently most actively used in home theaters, however, in fairness it should be noted that it is also quite popular in the professional environment.

So, the process of obtaining a volumetric 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 possible to implement on the basis of LCD, DLP and LCoS systems. However, given that the shutter method is used in home theaters quite recently, the developers still have to solve many questions. For example, the performance of LCD matrices does not yet fully meet the requests for refresh rate and response.

The device of projectors | Conclusions and perspectives

So, we got acquainted with the main projection technologies for the formation of theatrical format images, and also considered their features, advantages and disadvantages. Ten years ago, they were quite exotic display media that were just starting a massive assault on the home use sphere. Over the years, the image quality has reached a very high level, many technological shortcomings of early models have been overcome, and the variety of devices allows you to choose to your taste for very reasonable money. Even the suddenly emerging fashion for a three-dimensional image was immediately reflected in the produced models.

Today the situation is as follows. DLP is the most widespread technology. , built on micromirror panels, are found both in the inexpensive segment and on the average. In addition, this technology is also very promising, and for several reasons. First, the introduction of LED and laser light sources will help create mass projection devices that are highly miniaturized and low-power, with high luminous flux, excellent contrast, excellent color gamut and long lifespan. And, secondly, the high speed of such panels creates excellent opportunities for the implementation of high-speed methods of forming a three-dimensional image.

DLP's closest competitor is 3LCD technology. Although this circuit is not new, it is still very popular in both low-cost and mid-range devices. Moreover, despite the inherent limitations, for example, in contrast and 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 possibilities of this method of image formation has not yet been reached.

The technology of liquid crystals on silicon today is one of the highest quality in terms of picture parameters, however, and one of the most expensive, therefore such technology is used only in high-end home theaters. Nevertheless, such models become more affordable every year and even appear in the middle price segment, but in this parameter they are still very far from DLP- and LCD-.

Periodically, the question arises of the possible impact of the projected image on human health. It is believed that the picture formed using 3LCD and LCoS technologies does not have any negative aspects, since it is broadcast on the screen in a consolidated form, while DLP with one micromirror chip sequentially forms three multi-colored images at high speed. By the way, some studies show that 180 Hz frame rate is not enough to completely eliminate the "rainbow effect" and the 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 theaters, but also in the field of professional technology for concerts and light shows. We have already talked about the advantages that this technology gives, so it is worth saying a few words about the possible consequences. So far, the method of forming a picture using laser beams is not only very promising, but also very young, which means that there is practically no data on the possible effect on human health. Nevertheless, it has long been known that a laser beam with a radiation power of 1 mW can be hazardous to eyesight, which means that when using such a technique, the possibility of direct light flux hitting the audience must be completely excluded. In general, the issue of security remains to be investigated.

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

The choice of the best projector depends primarily on its purpose.

Features of home projectors

Home theater projectors must be able to display high-quality dynamic scenes (such as movies, videos, sports) and provide equally good results for different sources or signal standards. Unfortunately, the implementation of these features costs a lot of money, and for models with a "natural" resolution in 4K - they are completely inadequate.

Unsurprisingly, manufacturers are looking for various clever ways to obtain high definition pictures without the use of expensive full-fledged 4K chips. JVC calls this technology "e-Shift", Epson calls it "4K Enhancement", Texas Instruments calls it "XPR" (Optoma projectors). In principle, they all implement the idea of ​​optical shift of half-frames with subsequent superposition, just each in its own way. By the way, the benefit of such pseudo-4K is also when viewing less clear content. The same pixel grid (mosquito) dissolves almost completely. True, due to some loss of sharpness.

The specific requirement for home projectors can be minimum delay time- for gamers, this parameter is extremely important. Video format 3D is now capable of demonstrating the vast majority of models. The only thing that, to get a full-fledged home theater surround sound, you will have to buy a speaker system of the appropriate level.

Features of projectors for work and study

Educational goals and business needs involve working with static images. Hence, projectors for offices and classrooms most often they can easily do without complex subsystems of hardware and software interpolation and scaling, color management and other expensive chips. Their matrices are focused on "computer" resolutions, and "cinematic" ones are displayed with a significant truncation of the used area. It is clear that the latter does not affect the clarity of the resulting image in the best way. This group also has advanced functionality, but it takes specific forms. For example, support for interactive modes of operation.

General characteristics

The main interface for connecting projectors is HDMI, and many models are equipped with a couple of such connectors. If you have several signal sources, they will definitely not be superfluous.

Almost all projectors have learned to interact with smartphones and other devices using the MHL protocol. For convenient connection of portable equipment, they often have ports USB... Here, a useful functionality can be considered the ability to simultaneously charge mobile gadgets through this connector. It should be borne in mind that the presence of a USB interface does not mean the ability to work with flash drives. Such "buns" are only reserved for projectors with a built-in media player. Moreover, the latter is "smarter", the more video formats can be reproduced in offline.

Depending on the intended distance to the screen, projectors should be selected and along the "length" of the focus... The most short-focusing models are capable of forming a large diagonal image, being literally centimeters from a wall, canvas or board. On the other hand, such devices (as a rule) are not suitable for projection from a distance. Finally, the brightness of the resulting picture depends on a number of factors, the main among which can be considered the distance to the screen, the power of the emitted luminous flux and the level of illumination of the room. For most home theater projectors and partially shaded rooms, a flux of 1,500-2,000 lumens is sufficient.

We present to your attention a selection of very worthy and popular models for different purposes in the category of low-cost and mid-priced projectors earned in 2018 good feedback from buyers and experts. There cannot be completely universal solutions here, therefore, choosing the best projector for an office or for a home theater should be based on the range of tasks to be solved, as well as the expected conditions of its operation.

So, you are about to buy a multimedia projector, and the first question you have to ask is, why do I need it? It makes sense, isn't it? Well, let's try to explain. The first and main function of multimedia projectors (or video projectors, as they are also called) is to project an image from any device that generates a video signal during its operation (VCR, DVD player, computer, camcorder, etc.). The principle of operation of a multimedia projector is very similar to the principle of operation of a projector slide - the light emanating from the lamp passes through the block that forms the image (in a slide projector, this block is actually a slide, in a multimedia projector it is a set of rather complex devices, which we will talk about just below), and then the image is projected onto the screen through the lens. In this case, the size of the image can vary from 1 meter diagonally to 20 meters and even more. Thus, you can make a professional presentation with the demonstration of commercials, texts, graphs and tables, or you can turn your house or apartment into a home theater. All multimedia projectors have a set of characteristics that describe their capabilities and likely applications. The main characteristics are: luminous flux, resolution, imaging technology, weight. Let's start with weight. The weight of the projector determines its primary use. For example, if the projector will always be in one place, then its weight is not particularly important. If the projector needs to be moved from time to time (even when it comes to removing it from the table and into the closet), it is worth considering a more mobile projector. There is an established classification of multimedia projectors, which looks like this: Stationary projectors (weighing more than 10 kg) Portable projectors (weighing from 5 to 10 kg) Ultraportable projectors (weighing from 2 to 5 kg) Micro-portable projectors (weighing less than 2 kg) Naturally, the difference between these classes of projectors lies not only in weight, but also in functionality and technical capabilities. Portable multimedia projectors offer the maximum technical capabilities, quality and functionality inherent in portable models in general. Ultraportable projectors can achieve a reasonable compromise between functionality and mobility, and finally, microportable projectors, with very low weight and a set of the most necessary functions, are a real boon for business people who often travel around the world. The next important characteristic is the luminous flux. It determines how large the screen can be while maintaining acceptable image brightness. Also, the luminous flux determines how bright the lighting can be in the room in which the multimedia projector is used. The luminous flux is measured in Lumen (Lm). On this moment for micro-portable and ultra-portable models, the luminous flux ranges from 1100 to 2000 Lm. The luminous flux of 2000 Lm is enough to project bright images onto a 1.5 x 2 meter screen, regardless of the lighting (this is true for indoor work and provided that the screen is not exposed to direct sunlight). The upper bar of the luminous flux for portable models, and even more so for stationary ones, is already measured in tens of thousands of lumens. Today, in the production of multimedia projectors, mainly 2 image formation technologies are used. These are liquid crystal technology (LCD, Liquid Crystal Display) and digital light processing technology (DLP, Digital Light Processing). The general principle of LCD projectors is somewhat reminiscent of a film or slide projector, only instead of a film, a transparent liquid crystal panel is used, on which, using a digital electronic circuit a picture is created. The light from the lamp passes through the panel and lens, and an image is reproduced on the screen, magnified many times. In DLP projectors, light is reflected from the surface of a special chip (microcircuit) approximately 15x11 mm in size, on which there are about a million micromirrors that form an image and also enters the screen through the lens. To obtain a color image, LCD-projectors use three panels - for red, green and blue colors separately. In low-cost DLP projectors, the color components are projected onto the screen one by one at a high frequency (single-chip). Three micromirror component color chips are used in high quality, professional multimedia projectors. Each of these technologies has a number of its own advantages: LCD projectors are characterized by high luminous flux and high color saturation. DLP projectors are characterized by high image contrast, in addition, it is DLP technology that allows you to create ultra-lightweight unportable and micro-portable projectors. The smallest element that forms an image on an LCD panel or DLP chip is called a pixel. The number of pixels placed horizontally and vertically on an LCD panel or DLP chip determines the next characteristic of a projector - resolution. The resolution of the projectors is focused on computer video standards: most modern projectors have a resolution such as SVGA (800 x 600 pixels) or XGA (1024 x 768 pixels). Higher resolution SXGA (1280 x 1024) and UXGA (1600 x 1200) projectors are also available. A projector's resolution characterizes how detailed an image it is capable of displaying. The best image will be obtained if the resolution of the image from the computer matches the resolution of the LCD panel or DLP chip, at a higher or lower resolution, the image will be projected with little distortion.

You will surely face a difficult choice. For those who have not previously encountered this type of technology, it is difficult to navigate the huge assortment that stores offer and choose the best projector for specific purposes. In this article, we will cover the main types of projectors, as well as the most important characteristics projector and rooms to look for when choosing a device:

• Terms of Use
• Brightness
• Color quality
• Contrast
• Permission
• Installation methods
• Connectors and interfaces
• Network functionality
• Lamp resource
• 3D support
• Service Requirements

The post turned out to be voluminous, because we tried to collect all the information that may be needed when choosing a projector in one place and put it on the shelves.

Terms of Use

Projectors can be roughly divided into three classes according to the type of premises in which they are used.

The bulk of projectors are devices designed for use in offices, classrooms and classrooms and other areas in which usually there is light... The task of such projectors is to produce good picture despite artificial lighting. Of course, the lights can be turned off, but the ability of office and educational projectors to deliver high brightness has become imperative. These projectors are often referred to as “mobile” projectors because they are fairly easy to carry from place to place. Also, for such purposes, devices are offered classified as "education projectors" or "business projectors"

The second type of projectors is home theater projectors designed to work with the lights off. In these conditions, projectors do not require high brightness, but they are highly visible and highly valued for accurate color reproduction and high contrast levels.

Speaking of moviegoers, it is worth noting that recently, content in 4K format (4096 × 2160 and 3840 × 2160) has begun to appear, so High-End projectors that support such resolutions have already appeared. But they are extremely expensive! Fortunately, Epson has one that allows you to actually output 4K content. with full HD matrix... We call it "4K Enhancement". For those who have not yet heard the principle of such technology, I will explain that the essence of "4K enhancement" is approximately as follows: every second frame of the image is shifted by half a pixel diagonally, as a result of which each pixel is divided into four subpixels:

Essentially, a 4K visual field is created. While every single pixel of this field cannot be controlled, it is still possible to extract details from native 4K content that would not be possible to display on a full HD or WUXGA projector. Ask "why"? I answer: to be able to display 4K content without a huge overpayment... After all, now you can buy a projector that costs a little more than a model with full HD resolution, but is able to actually display 4K content, and not release a model with real 4K matrices, which will cost "like an airplane." More precisely, it is possible to produce something, but only a few can afford them.

Many home theater projectors offer functionality that makes images visually clearer while staying within the projector's available resolution. For example, Epson calls this function "Super Resolution". We call it among ourselves "Unsharp Mask", by the name of the filter of the same name from Adobe photoshop: and the sharpness is increased, and the micro-contrast on the transitions between areas of the image, which visually, in fact, increases the perceived sharpness of the image.

Installation and room parameters

Perhaps this is where the article should begin. Each projector has a parameter called the "throw ratio" or "throw ratio" that specifies the ratio of the distance from the projector to the screen to the width of the screen.

Projectors with a high throw ratio are called long focus... For example, with a ratio of 2.0: 1, the projector will give you an image that is 2 meters wide from a distance of 4 meters. Do you have enough wall lengths? Are there objects within 4 meters of the screen that would make it difficult to install the projector in that location?

Projectors with a small throw ratio are considered short throw... For example, Epson refers to projectors with a throw ratio of 0.55: 1 as short throw, while other manufacturers sometimes refer to projectors with a throw ratio of less than 1.5: 1 as short throw.

Fast installation

Sometimes it is required to deploy in the shortest possible time mobile screen and adjust the image. In this case, the projector may be located below the required level, for example, on a pedestal, and not on a table. If you look at the screen at an angle other than 90 degrees, the projector image is distorted and becomes trapezoidal instead of rectangular. To quickly fix this problem, "keystone" is used. This function is, perhaps, all projectors, and it can be controlled directly from the control panel built into the projector. In addition to vertical, there is also horizontal geometry correction, which allows you to position the projector to the left or right of the center of the screen. Most Epson projectors have both, which automatically makes the Quick Corner function available, which allows you to adjust the shape of the screen by changing the position of its four corners.

Many projectors are equipped with automatic vertical geometry correction.

Some Epson projectors have additional features to make installation easier. "Screen Fit" allows you to identify the screen with a black frame and instantly adjust the geometry with a single press of a button. Focus Help allows you to perfectly focus the lens without running from projector to screen.

Of course, these functions lead to some deterioration in the clarity of the image, but not to such an extent that they significantly lose their attractiveness, and the text - readability.

Connectors and interfaces

Most projectors come standard with HDMI and VGA connectors. Both allow you to receive signals up to 1080p without any problems. However, if you want to display 3D in Blu-ray 3D format, HDMI version 1.4 or higher is required.

Most projectors, other than premium installation and home projectors, have built-in audio. In most cases, we are talking about one speaker with a power of 2 to 16 watts (the more - the louder). If you do not have an external sound system at hand, then you can transfer sound to the projector either together with video via HDMI, or separately, for which you will need an Audio In connector. In turn, the audio input can be either RCA (tulip) or 3.5mm minijack, like a headphone. Education projectors can also be equipped with a microphone input.

A number of projectors have weekend VGA and audio connectors (VGA Out, Audio Out), which allow transmitting the signal further to other devices, allowing the projector to act as a splitter. USB connectors can play different roles:

• Connecting your document camera
• Connecting USB storage devices
• Transferring video and sound from a computer
• Transferring mouse signals to the computer (from the buttons on the remote control or from interactive projectors)

In general, it is often impossible to understand the USB functionality without reading the instructions. For example, if external media connectivity is supported, what file formats can the projector play? USB inputs can also be of various formats - Type A (like in flash drives), Type B (like in printers), mini-USB.

In education, old connectors such as RCA (Tulip) and S-Video may be in demand.

Popular with installation projectors is the HDBaseT interface, which allows video and other information to be transmitted over long distances using a cheap cat5 / 6 network cable.

Networking capabilities

By connecting a projector to an organization's network, you can solve two problems: the first is to remotely control the projectors and monitor their status using a special software... The second is using the projector as a shared one and transferring the image to it over the network.

It is also possible to project over a wireless network from mobile devices. For details, see "Networking Capabilities of Epson Projectors". Another option for connecting mobile devices is via HDMI with MHL support. This connection option allows you to duplicate the screen on the projector mobile device(if it supports MHL).

Lamp resource

Manufacturers always publish an estimated lamp life for the lamp used in their projector. The projector itself can use the lamp in "Normal" or "Eco" mode. The brightness of the latter, as a rule, is lower by about 20-30%, but this leads to a longer lamp life. Also, many Epson projectors have the "A / V mute" function, which allows you to interrupt the presentation for a while without turning off the projector. In this mode, the lamp is temporarily dimmed by 70%. For modern projectors, especially those used in education and business, the cost of replacing the lamp is not very high, but it still has to be borne in mind, especially when purchasing a batch of projectors.

The presence of an air filter, which prevents dust from entering the lamp, has a positive effect on the lamp life. By the way, the cooling system and the mode in which the lamp is used also affect the noise level of the projector. It is especially important to take this parameter into account in small spaces and rooms.

But not a single lamp! Since 2015, the Epson catalog has a wide range of laser projectors... Those. projectors with a laser light source. Their main advantage: light source resource 20,000 hours or more! The first sign was, and then there were a whole series of laser projectors for a variety of tasks: and even the unusual Epson LightScene EV-100, made in the form of a spotlight... These projectors, among other things, also differ in the ability to install in any position.

The appearance of more budgetary, "home" laser projectors in the catalog is now only a matter of time.

3D support

When displaying 3D from a computer, you need to make sure that the projector supports the stereo pair format you are sending to it. Examples of formats are "top-bottom", "side-by-side", "frame packing". To display 3D Blu-ray discs, HDMI version 1.4 or higher is required.

3D is supported to varying degrees by many projectors, although best quality provide devices specially designed for this task. Any 3D technology works due to the fact that an image not intended for it is hidden from each eye. For example, active glasses in turn cover the left or right eye with an LCD screen. This leads to a multiple drop in the brightness of the 3D image, which is the main problem of any 3D system. By combining the projector's inherently high maximum and color brightness, and 480Hz Epson active glasses technology to reduce the amount of time that both flaps are closed, Epson 3D projectors provide brighter, more vivid 3D images.

Note from 03/04/2019- system of paired projects discontinued and no longer sold, because we can safely assume that the "era of 3D renaissance" has successfully ended and the vast majority of buyers (including in the field of business and installation) projectors with 3D are simply uninteresting... Therefore, at the moment in the range of Epson, only 3D home theater projectors.

To be fair, I'll tell you that back in 2016, there was still another interesting solution, originally designed for 3D - the Epson EB-W16SK system of two twin projectors EB-W16. Unlike conventional projectors, it used not active, but passive 3D glasses technology based on polarizing filters. Although the EB-W16SK system was more expensive than a separate 3D projector, and the passive technology required a dedicated screen, the savings came from the purchase of cheap passive glasses (good active glasses cost around $ 100). For this reason, the EB-16SK was a good choice in cases where it was necessary to demonstrate 3D to an entire class.

Projector Maintenance Requirements

Finally, let's talk about such an important component of the projector as the dust filter. Many manufacturers claim that their projectors do not have filters that require cleaning and replacement, which means there is no other consumable. But they are silent about the fact that the presence of a dust filter helps to extend the life of the projector and avoid high repair costs. For comparison, DLP projectors can only be cleaned of dust in the service department for money, and anyone can clean the removable filter of a 3LCD projector at home. The filters should be cleaned at least every three months.

Instead of output

We hope that, taking into account all the recommendations from this post, you can do right choice, and then the projector will not only help you in your work, but will also bring you a lot of joy, good mood and an unforgettable experience of watching movies and games on the big screen.