South Korean researchers have designed and built an inexpensive optical lens that collects light from a large area and produces a virtually distortion-free wide-angle image. Standing in contrast to commonly known "fisheye" lenses, which produce significant amounts of visual distortion, low-distortion wide-angle lenses can potentially improve image-based applications such as security-camera systems and robot navigation.
The new wide-angle lens is lighter, smaller and more affordable than commercially available "rectilinear" lenses, which also produce low-distortion views. The researchers present their new feat of optical technology in the Dec. 1 issue of Applied Optics, a publication of the Optical Society of America.
Made of inexpensive components and available for little more than $100, the new wide-angle lens has been designed specifically to improve indoor security.
"For spacious places with high ceilings such as factories, hotels, theaters, resorts, and auditoriums, the lens can capture the entire floor and this will help security personnel to easily monitor those places," says lead author Gyeong-il Kweon of Homan University in South Korea. In this scenario, the lens would be attached to inexpensive, commercially available bullet cameras, he says.
The principle of a wide-angle lens is simple, according to Kweon.
"Think about holding an immaculate silver spoon above your head and looking up," he says. "Then you will notice that the entire room can be seen from the reflections on the spoon."
But there's a problem, he points out.
The reflected image from the spoon is severely distorted. For example, straight lines become curved, and the distances between objects become skewed. The challenge is to design a lens that collects light from a wide area (i.e., from the entire room) and yields an image that is "perspectively correct," in that it accurately depicts the shapes and relative dimensions of imaged objects.
"The most creative part of our work was the discovery of the right shape of the spoon which gives a perspectively correct image of the room," Kweon says.
An elegant piece of optics technology, the new lens looks like a snow globe in the shape of the U.S. Capitol dome. Light from a large area enters the dome of the lens and encounters a v-shaped mirror. This reflective lens then redirects the light rays to a second lens that resembles the slender statue atop the Capitol dome. This "refractive" lens produces a sharp image of the large area at the exact location of the image sensor within the bullet camera.
The v-shaped lens is called a catoptric (reflective) lens and the second lens is known as a dioptric (refractive) lens, so the combined design is called a "catadioptric" lens.
"Ingenious catadioptric lenses having similar characteristics have been designed by other researchers," says Kweon. However, he says, "those lenses were optically inefficient and were mostly of academic interest."
In contrast, this new design delivers straightforward, practical wide-angle images, producing a "field of view" (FOV) of 151 degrees. The FOV from this technology can be increased to 160 degrees by adding a little more complexity, Kweon says. A FOV of 180 degrees would mean capturing everything that you see in front of you, as well as on your left and right sides. Mathematically, this is the upper limit of what is possible with rectilinear imaging, the kind of imaging that renders straight lines as straight rather than being curved and distorted. By comparison, the human eye has a field of view of approximately 46 degrees.
Some fish-eye lenses have a FOV that exceeds 180 degrees. However, they suffer from "barrel distortion," in which lines are stretched outward. In a fish-eye picture of a jail cell, for example, the metal bars would appear stretched outward, as if a cartoon character had pulled them apart.
Rectilinear lenses, those that produce images without such distortions, are commercially available. However, for technical reasons, these models have a limited field of view, of typically less than 120 degrees. Also, they are bulky, large, and very expensive, costing more than $1,000.
While the new design does not have the FOV of some fisheye lenses, there is no shortage of useful applications for wide-angle cameras with an FOV of less than 180 degrees. One possible application, Kweon says, is to use the lens as an ingredient of intelligent security systems. In this scenario, the new catadioptric lens would capture a large swath of space, and a camera with "pan-tilt" ability would zoom in on the region of interest (ROI), such as the location of an intruder. This can be more effective, Kweon says, than a multitude of cameras watching their respective ROIs.
The new lens is relatively small and commercially available through a South Korean company called Nanophotonics (www.nanophotonics.co.kr) that Kweon has started up.
In addition to improving security cameras, many other indoor applications are possible, Kweon says. One possibility, he says, is as a robot navigational aid. "When this lens is installed on a ceiling, the room is captured in a perspectively correct manner. In other words, the captured image is a scaled version of the room. Therefore it is easier to estimate distances and object sizes, and it can help home robots to effectively navigate the room," he says.
With much promise for strengthening image quality, there is one area the researchers are focusing on for improvement: the camera itself unavoidably shows up as a small circle in the center of images, a phenomenon called "central obscuration." By removing the catoptric (reflective) lens, Kweon and his research partner Milton Laikin, a renowned lens-design expert from Los Angeles, have designed another lens that eliminates this problem, but has a narrower field of view, at approximately 120 degrees so far.
Due to its tiny size and delicacy, the current lens can only be used indoors but according to Kweon, it is easy to improve upon this first step and create a larger lens for outdoor commercial needs. "This lens is designed for a bullet camera," he says. "Since a bullet camera is really tiny, I think this imaging system cannot endure the harsh outdoor environment."
"An outdoor version can be made for a larger camera and this lens could be installed on intersections to monitor traffic violations and pedestrians."
"Because it uses a mirror, it is easy to translate the lens design for other wavelengths, such as the infrared," he says. Wide-angle lenses in these other wavelengths have other potential applications, such as wild-fire monitoring and human search-and-rescue.
Airborne thermometer to measure Arctic temperatures
11.01.2017 | Moscow Institute of Physics and Technology
Next-generation optics offer the widest real-time views of vast regions of the sun
11.01.2017 | New Jersey Institute of Technology
Among the general public, solar thermal energy is currently associated with dark blue, rectangular collectors on building roofs. Technologies are needed for aesthetically high quality architecture which offer the architect more room for manoeuvre when it comes to low- and plus-energy buildings. With the “ArKol” project, researchers at Fraunhofer ISE together with partners are currently developing two façade collectors for solar thermal energy generation, which permit a high degree of design flexibility: a strip collector for opaque façade sections and a solar thermal blind for transparent sections. The current state of the two developments will be presented at the BAU 2017 trade fair.
As part of the “ArKol – development of architecturally highly integrated façade collectors with heat pipes” project, Fraunhofer ISE together with its partners...
At TU Wien, an alternative for resource intensive formwork for the construction of concrete domes was developed. It is now used in a test dome for the Austrian Federal Railways Infrastructure (ÖBB Infrastruktur).
Concrete shells are efficient structures, but not very resource efficient. The formwork for the construction of concrete domes alone requires a high amount of...
Many pathogens use certain sugar compounds from their host to help conceal themselves against the immune system. Scientists at the University of Bonn have now, in cooperation with researchers at the University of York in the United Kingdom, analyzed the dynamics of a bacterial molecule that is involved in this process. They demonstrate that the protein grabs onto the sugar molecule with a Pac Man-like chewing motion and holds it until it can be used. Their results could help design therapeutics that could make the protein poorer at grabbing and holding and hence compromise the pathogen in the host. The study has now been published in “Biophysical Journal”.
The cells of the mouth, nose and intestinal mucosa produce large quantities of a chemical called sialic acid. Many bacteria possess a special transport system...
UMD, NOAA collaboration demonstrates suitability of in-orbit datasets for weather satellite calibration
"Traffic and weather, together on the hour!" blasts your local radio station, while your smartphone knows the weather halfway across the world. A network of...
Fiber-reinforced plastics (FRP) are frequently used in the aeronautic and automobile industry. However, the repair of workpieces made of these composite materials is often less profitable than exchanging the part. In order to increase the lifetime of FRP parts and to make them more eco-efficient, the Laser Zentrum Hannover e.V. (LZH) and the Apodius GmbH want to combine a new measuring device for fiber layer orientation with an innovative laser-based repair process.
Defects in FRP pieces may be production or operation-related. Whether or not repair is cost-effective depends on the geometry of the defective area, the tools...
10.01.2017 | Event News
09.01.2017 | Event News
05.01.2017 | Event News
16.01.2017 | Trade Fair News
16.01.2017 | Automotive Engineering
16.01.2017 | Life Sciences