【 Weak current College 】 orthography and projection of knowledge-Power By 【 China power house network 】

Currently, both the mobile small business presentations, multimedia conference rooms, classrooms, sports facilities, churches, business establishments, large auditorium of the medium, and large projection system, virtual shows even greater to the cinema of large-screen projection systems, either they will adopt front projection or rear projection methods used, in addition there seems to be no third projection mode. Before the vote and rear-projection can be said is that all of the projection technology. The so-called front projection, simply put, is the projector installation location and audience in the same side of the screen, projector Ray issued to the screen, the screen form the image, and then the reflection of light to the eyes again. Similarly, the so-called projection, projector installation location and audience are located on the second side of the screen, a light projector from each side of the screen to the screen, the light through the screen into the audience's eyes. Front projection screen can be made of any size, but need to control the ambient light in order to get a good viewing. Very useful when there is a lot of viewers of anechoic chamber environment. Rear projection screens in size as before, but do not need to control the ambient light. Comparison applies to viewers, the ambient light and the lighting is very good for the environment. From the development of history, the history of the vote before very long, since the film and slides before the vote since. Rear-projection history is relatively short, only for the last 20 years, however, but the projection project has brought the world a whole new concept. Backlight can be projected out a TV image quality the same screen size, but could be extended to the TV set hundreds of times. Before the vote and rear-projection of each applicable occasions ideal projection environment is basically no lighting lights and use very bright projector. If the ambient light is very bright, the vote will appear before the dark, at this time, the rear projection is the best choice. However, in order to optimize the quality of the projection in the installation of rear-projection screen is used, the requirements of space than the larger before the vote, and installation projector space to dark enough. David Hull said: "before the vote is suitable for rear projection provides projection space. " Sudden, not prepared room is used for a very good example, as in a business presentation or general meeting, a large group of people as a special topic drastic in a smaller room. If the number in the 50 to 100, with a smaller screen is enough, no need to use a larger screen. Howard Sinkoff said: "the front-projection screen can be made of any size, front projection advantage is only a front projection screen, you can do it very much, just like a cinema screen. " But before the vote off the projection room required bulbs get looks very comfortable image, like the cinema, the need to control the ambient light, very useful when there is a lot of viewers of anechoic chamber environment. Rear projection is a preferred choice and a better way of projection, however, due to the projection space, many environments are not used. In addition, rear-projection screen size is limited, but does not need to control the ambient light. Comparison applies to viewers not much light lighting very good environment. David Hull said: "the best application of rear-projection: audience of more than 100 people, a presenter with ju space behind the screen and projector setup can install a complete rear projection screen. " Like a classroom and multimedia conference room such a place is probably not installed rear projection system with the required space. However, many larger presentation, especially in the great Hall and even outdoors, with suitable projection to several high-quality rear projection screens, rear projection is used. Anjum says: "like the sports ground is not possible to turn off the lights, you must open a bright light to see the game, the majority of people in the playground will select backlight, because only the rear projection to a clear, bright image type. "" Vote for the cinema, the former is preferred, it is like to have to think, because cinema screen size is too wide and too much, and if you are behind in the movie screen to provide a space for rear projection room, that's a waste of space, or too expensive. Ng: the "Stevie" at school, because in the Church in need only be able to see images, students to show the image quality of the environment, requires lower, while saving space and equipment costs, which generally do not select backlight. "If the user's budget and the available space is low, narrow front projection, it is a unique programme, for rear projection used space is relatively little, if customers have to a large, wide effects, such as the cinema effect, then only select voted before, because only the first vote to a single screen to meet his requirements. Projection screen technology classification screen from the projection mode is divided into front projection screen (reflective) and rear-projection screen (transmission) of the second class. As the projection screen is not affected by the size limit (customizable), but will be affected by the ambient light effects causing screen contrast of serious decline. Rear-projection screen picture overall sense of strong, is not affected by the environmental effects of light, can accurately reflect the information quality, colorful pictures, vivid, currently the largest single optical projection screen 200 inches, valid image range 4034mm * high 3018mm. Positive projection screen with a rear projection screen from optical structure is divided into the following categories: is: bent screen-projection screen (metal-arc type curtain), a flat screen (bead curtain/metal soft curtain/white screen)
Rear-projection screen: rigid rear-projection screen (transmission curtain), soft rear-projectionscreen (transmission screen)
Front projection plane screen gain is relatively small, viewing angle is large, light must be weaker; arc-shaped scene gain greater angle smaller ambient light can be strong, but the screen is reflective of the incident light in all directions, and focus on high temperature easily screen color distortion. From texture are divided into glass curtain, metal curtain, embossed plastic curtain, etc. Projection screen with optical projection screen, scattering-screen and soft rear projection screen of classification, a principle different rear projection screen are to overcome the many positive vote the way disadvantage: projector installed on a screen behind the darkroom, the decoration will not cause disorders, also masks the projector running noise, while not susceptible to interference from ambient light. Scattering-screen depend on the scattering particles to complete projection light distribution, scattering-screen has the following significant disadvantages: low energy usage, waste projector brightness output
Bright spot effects (effects of the Sun), brightness uniformity difference
Color drift phenomenon seriously, the contrast is very low
The Visual angle is small, does not apply to the wide range of imaging
Scattering-screen market application not optical projection screen depend on the micro-optical body to complete projection light distribution, is now recognized as best in display mode, Fresnel (Fresnel) lens technology is widely used in optical screen manufacturing process, the Fresnel lens structure can be the incident light into parallel rays of light, in a certain angle range Ho screen brightness. Cylindrical lens technology is widely used in the manufacturing technology of optical screen, the screen on the front of the cylindrical lens structure, you can control the horizontal and vertical light distribution, has expanded the scope of the feature from the perspective of, + customers can according to the actual application environments, design projection optics and screen focus maximum angle, in order to achieve the best coverage angle of the light path.　　Optical projection screen of the only drawback is that in order to best focus, you must select a focal length range match projector lens (projection distance is required). Most optical projection screen with multiple focal length optional, covering most of the projector's lens focal length range. Rear-projection using soft screen high light transmission rate of cellophane spray forming rear projection to soft screen with affordable, seamless (dimensions can be customized), transport, easy to install (you can collapse), the projector lens is not requested, etc., usually applied in the leasing industry. Rear-projection screen because it is a soft application of light reflectance of imaging, inevitable there diffuse screen brightness uniformity of weakness: weak, serious effects "," solar energy utilization is low, color drift phenomenon seriously, the Visual angle is small, and so on. Low resolution and low contrast backlight soft screen displays the data do not suit the application. At the same time, in the production of materials for physical characteristics, soft rear projection screen has the following disadvantages: stability vulnerable to temperature, humidity and airflow resulting image flickers
Prone to wrinkling, discoloration, variant, mildew, ageing, quality guarantee period is short
In order to guarantee video scope (typically a nominal 160?), gain low (usually marked as 1.5 left-right)
Rear-projection installation is more complex, the former for relatively simple rear projection installation is more complex, since not all projection environment has enough projection distance ideal projection effects. Stevie Ng said: "rear-projection system with a complex installation process, this includes installation screen wall design, also suitable for handling rear-projection screen housing structure; e.g., doorwidth, elevators, etc. The installation also requires professionals, is more complex. Before the vote on the "projection distance limitations is small. As the concept is said before vote, vote system before the projector installation position relative to the screen is in the audience at the same side, front projection system projector installation space is already in the area of audio-visual space, does not require additional display space. Front projection system installation and placement of projector is relatively simple, in a screen placed in front of a projector.　　Most people know how to design such a system. Design easy and intuitive. Howard Sinkoff said: "for rear projection screen, installation projector space must be black. Ensure that the projector's space all black light than the control environment is more important, for the first vote, you must control the ambient light, but not all black, bright screen (SILVER or VUTEC 6.0 gain of SILVER STAR) does not require strict control of ambient light. Rear-projection of the projection distance can be less than immediate former vote if the projector to the screen projection image, then the former cast and rear-projection space are the same. If rear projection system with reflex system, and that the necessary space can be as small as possible. The most typical example is the rear projection TV, the thickness of only 50 to 60 inches. Rear-projection screen-projection screen before the transparent, opaque white front projection screen or gray, because it will make light reflected back to the audience's eyes, so it is not transparent. Rear-projection screen is transparent, rear-projection screen there is a second option, a slow reflection screen, one is the optical screen appear, they are different. Optical screen absorption from the projector light is evenly to the audience. Light evenly distribution center and corner of the screen. Slow reflection screen is a common and transparent glue plate or glass layer, butit added some diffuse reflectance materials. 　　Slow reflection screen display of the image whose light is evenly to the audience's eyes, and is irregularly spread in all directions, solar effects are very powerful, comparison and dark corners. Front projection screen quality environment, rear-projection affected small. Before the vote of the entire screen effects from environmental effects of light, the light is very big; rear projection is not affected by such a large impact. Stevie Ng said: "people see front projection screen is not only the projector is projected onto the screen and then the reflection of light to the eyes, people can see an image are due before a vote or two above synthesis of light; one is projecting out the screen projector reflection to the eyes of light; the other is the ambient light reflection on the screen to light the human eye; the second is more reflective light, front projection mode, if the screen there is a light around. This lamp lights will hit the screen, the light reflected by the screen to the human eye, the synthesis of results will influence the quality of the viewing screen, even before the vote turned off all the lights in the environment, let the room into a dark, but the projector light hit the screen, the screen will be the reflection of light hitting the ceiling, ceiling is white, the rays will go through reflection to return to the screen. So the pictures are affected. Projector light reflection like audio echo, a trumpet sound hitting the wall, and then from the wall back to the user, the walls will affect the tone. Projector reflection principle almost, the projector will light hit the screen, then hit the walls from the screen, then to the human eye, this procedure will make the picture effect is affected. However, the rear projection system in this regard would not be affected by what impact, if any, do not like such a big front projection. "Former vote is not suitable for speaker stands in front of a screen cast,prior to use in presentations, explain the process is not very convenient: the speaker can't stand in front of the screen, the speaker will not only block the light, the shadow to the screen; in addition, the former cast light into playAbout people's eyes, eyes on the speaker is very harmful. Backlight will not be affected by this impact. Stevie Ng said: "most used in rear-projection screen to achieve better take effect, or while it was in the previous explanations, application of occasions; such as meeting rooms, control center, audiovisual Centre.