[Analysis of the imaging principle of the Fresnel optical screen from a technical point of view] Projection screen technology introduction
Rear projection optical screens are currently widely used in large conference rooms, command and control centers, training and education, video conferences, exhibition halls, exhibition halls, auditoriums, stadiums, concert halls, supermarkets, airports, stations, terminals, cafeterias, shop windows, etc. , And even complex environments with strong ambient light. So what exactly are optical screens and Fresnel optical screens, how do they image, and what is the difference between traditional projection screens?
1. Definition of optical screen
A projection screen containing one or more optical lens systems is called an optical screen. In the lens, the light is refracted and the direction is changed. Only the rear projection screen can control the direction of the light, so only the rear projection screen has optics. Screen. The direction of the light depends on the refractive index of the projection screen material and the cross-sectional shape of the lens.
2. What are the optical rear projection screens on the market?
At present, the main Fresnel optical screens on the market are the GWA giant wide-angle screen of Denmark DNP company/NWA new wide-angle screen/Holo Screen/SIGMA Sigma screen, Stewart company of the United States/Rear-projection diffuse reflection hard screen/BlackHawk Xtreme NEW /MicroWave rear-projection optical screen/PowerView rear-projection optical screen/OptaWave rear-projection optical screen, WA1806 rear-projection optical screen of Denmark SVS company/vision2000 anti-slip optical screen, FL optical screen of Chengdu FSCREEN First company.
Denmark DNP is the most famous Fresnel optical screen manufacturer in the world. Below we mainly use DND Fresnel optical screen as a sample to explain the optical principle of the device. The basic principles of other companies are similar.
3, optical Fresnel lens
The difference between a traditional lens and a Fresnel lens is shown in the figure below:
In the Fresnel lens, only the curved surface is the effective part of the lens. If you remove the other parts and flatten the effective lens part (as shown in the picture on the right), you will get a Fresnel lens. The lens is cut by a CAD/CAM processing center with diamonds. There are as many as 10,000 different lens profiles on one screen. The investment in rear projection screen molds is huge. DNP is the only rear projection screen manufacturer with its own mold factory. Therefore, each series of DNP products has a different focal length; the size of each section u003d the dot pitch (resolution) of the screen.
4. Schematic diagram of the working principle of Fresnel lens and cylindrical lens and the working principle after combination
The combination of Fresnel and cylindrical lenses can achieve a horizontal viewing angle of 180 degrees, and the wide-angle series of DNP screens thus gain a huge market share in the world. It has become the most popular projection screen on the market for many years, suitable for various applications.
The combination of Fresnel and fog lens is also one of DNP's nine screen series. It is specially developed for some special applications and has been put on the market a few years ago. However, because the viewing angle is not as good as the wide-angle screen series, the applicable area is narrow, DNP company only uses it as a supplementary product.
5. The difference between a double-layer screen and a single-layer screen, the double-layer screen has the following characteristics:
It has better brightness uniformity from center to corner than single-layer screen;
Very suitable for short-distance projection
Very suitable for multi-screen splicing.
6. The working principle diagram of the two filter systems of DNP's double-layer screen to increase the contrast
The first type: the optical principle of high-contrast cylindrical lens:
(UCS/RUCS screen) The surface of the optical lens between the two lenses is covered with a layer of melanin, which can absorb ambient light. The cylindrical lens can pick up the light from the projector and transmit it to the viewer. The ambient light will be absorbed.
The second type: the optical principle of high-contrast glass beads:
(BB screen) This technology uses fine black glass beads and sprays a layer of melanin on one side. The black glass beads can pick up the light from the projector and transmit it to the viewer. The ambient light on the screen is directly absorbed
The above briefly introduces the imaging principle of optical rear projection screens. With the development of projection screen technology, we see that many 'front projection optical screens' have also been introduced on the market. Generally speaking, the color performance of rear projection screens is better than The front projection is better, but relatively speaking, its installation is more complicated than the front projection screen.