Night scopes, or night vision devices, are used to intensify human sight under very low light conditions. There are several types of night vision scopes. Infrared imaging systems, also referred to as "active" night vision devices, focus infrared light on a scene. Infrared is beyond the light spectrum visible to humans, so the beam itself is undetectable. Image-converting technology transforms the scene illuminated by the infrared into a visible image. Thermal imaging systems work in a similar way, converting the pattern of heat emitted by objects, people, or animals into a visual image. The night vision devices perfected for wartime use and also available commercially today are called "passive" night vision systems. These systems amplify images picked up in minimal light, such as starlight, into visible images. The view through a passive night vision device may be from 20,000 to 50,000 times brighter than what the unaided eye could see.
Night vision devices were developed for military use, where seeing in the dark is an obvious tactical advantage. The United States used night vision devices in the Vietnam War and to great effectiveness in the Persian Gulf War. Night vision devices are also used by both urban and rural police forces. In the late 1990s, night vision devices were finding more commercial outlets. They began appearing in some high-end cars and are being marketed directly to consumers for recreational use.
Research into night vision devices began in the 1940s. The United States military established a night vision technology development program by the late 1940s, and by the 1950s had come up with viable infrared viewing systems. This was an active technology, meaning it used a directed beam of infrared light. Though the beam itself was invisible to the unaided eye, opponents armed with equivalent technology could easily pick up the beam. The infrared viewers used in the 1950s and 1960s are referred to as "Generation 0" technology.
ITT Corporation (now MIT Industries, Inc.) in Roanoke, Virginia, began producing night vision devices for the United States military in 1958. The United States Department of Defense founded its own Night Vision Laboratory in 1965, dedicated to improving the existing technology. During the 1960s, scientists developed the first workable passive night vision systems. These devices were called "Starlight" systems because they were able to pick up and amplify images seen only by starlight. They are also known as "Generation I" devices. They actually worked best in moonlight. Generation 1 night vision devices were used in combat for the first time during the Vietnam War.
Improved technology developed shortly after the war led to smaller, less bulky night vision devices with better resolution. These more reliable instruments were called "Generation 2." The United States military continued to develop and refine night vision technology during the 1970s and 1980s, fitting weapon sights with night vision targeting devices and training pilots in night vision goggles. Passive Generation 2 devices were able to produce a good visible image in very low light situations.
"Generation 3" technology was developed in the late 1980s. These new night vision devices used gallium arsenide for the photo cathode material inside the image intensifier tube. This produced better resolution even in extremely low light situations. United States forces used night vision devices extensively in the Persian Gulf War, where the technology allowed troops to see not only in the dark but through dust and smoke as well. By the late 1990s, the Department of Defense had reduced its funding for night vision development, and some manufacturers began searching for consumer markets for the gear. Individuals may buy night vision devices in the United States, but their export is still restricted.
The image intensifier tube, which is the main working component of a night vision device, is made up of millions of hair-fine fibers of optic glass. The glass used is a particular formula that preserves its desired characteristics when heated and drawn. Optical quality glass is used for the eyepiece and output window. (The output window is an ocular lens, like the eyepiece of traditional binoculars.) Other materials used in the image intensifier tube are phosphor and gallium arsenide. The tube body is composed of metal and ceramic, and the metals used may be aluminum, chromium, and indium.
Passive night vision devices work by sending light through a lens, an image intensifying tube, and another lens. Light enters through a lens called the objective lens, which is similar to a fine camera lens. The lens focuses the light into the image intensifier tube.
The tube is the most complex piece of the night vision device. It is handmade to exact specifications. The tube is a vacuum tube with a photo cathode, a power source, a microchannel plate, and a phosphor screen (the screen emits light when excited by electrons). The cathode absorbs light (photons) and converts the photons into electrons. The electrons are multiplied thousands of times as they pass down the tube, by a wafer-thin instrument called a microchannel plate.
A standard microchannel plate is 1 in (25 mm) in diameter and about 0.04 in (1 mm) thick—about the size of a quarter. Incorporated into this plate are millions of microscopic glass tubes, or channels. The latest night vision microchannel plates contain over 10 million channels. These channels release more electrons as the electrons bounce through the tubes. The channels must be uniform in diameter and spacing on the plate in order to produce a clear image. The electrons then hit a phosphor screen. The phosphor screen reconverts the electron image into a light image, and focuses it on the output window.
The entire image intensifying tube may vary in size, but the finished tube can be small enough to fit into a gun sight or into a pair of military goggles. For example, a current product available from ITT is a Generation 3 monocular that is 4.5 in (11 cm) long, 2 in (5 cm) wide, and 2.25 in (5.5 cm) high, including both lenses. The entire instrument weighs 13.8 oz (0.4 kg).
The manufacturing process for night vision devices is complex. Over 400 different steps are needed to make the core component, the image intensifier tube. Manufacturers carry out several major process steps simultaneously in different sections of the plant.
Quality control at every step of the manufacturing process is essential for the image intensifier tubes to work correctly. Large manufacturers have honed the process so that each step is tested or gauged, and workers are unable to move the part onto the next step if the part has not met the quality control requirements. Manufacturers use sophisticated calibration equipment to measure such things as the diameter of the glass fiber, the thickness of the microchannel plates, and the temperatures in the various furnaces. Materials supplied by subcontractors are checked as they come into the plant. The calibration equipment used for testing is itself tested frequently for accuracy.
The final product is tested in various ways to ensure that each device works as it should. Each device is checked for its visual action. Other tests may show how tough the device is under adverse conditions. Finished night vision devices may be tested for how they respond to shock and vibration, and there may be a drop test. For some military requirements, the devices may be subjected to days of extreme heat and humidity.
The manufacture of night vision devices can result in some hazardous waste, as many chemicals are used in cleaning and etching. However, some manufacturers have been able to substitute less toxic or nontoxic chemicals for harmful ones, and in general the manufacturing process now is cleaner than it was when the technology was first developed. Image intensifier tubes are expensive and arduous to produce, so manufacturers try to salvage as much scrap as possible. If a tube is built that does not function, it would be disassembled and the parts reused.
The night vision industry is making itself available to the non-military consumer market. While prices are still high, as demand increases, the price may decrease until the technology is fairly affordable. The technology is already being used by law enforcement and search-and-rescue teams. As the products become more in the price range of consumers, and because the images viewed can be recorded by video cameras or as photographs, more photographers, wildlife watchers, boaters, campers, and many others may begin to use night vision technology in more innovative ways.
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