Night vision device
A night vision device , and night vision goggles ( English night vision goggles ) is a technical apparatus, the visual perception in the dark or half-light enables or improves.
Night vision devices are used by naturalists , hunters , the military , the police, security services and also by private individuals. Night vision devices are also suitable for monitoring the radiation from operating in the infrared range lasers .
functionality
There are various methods that enable or improve vision in the dark or in very low light.
- By amplifying the weak light that is present, see also image intensifier
- By converting (invisible) infrared radiation ( near infrared , NIR) from the environment into visible light ( image converter tube , semiconductor image sensor ). This method can be supplemented by lighting with infrared spotlights.
- By making the thermal radiation (infrared radiation in the MIR range) visible from the objects themselves when their temperature deviates from the surroundings. The wavelength of this infrared radiation is 5–15 µm and can be recorded with thermal imaging cameras . The method is particularly suitable for observing warm-blooded creatures, freshly parked vehicles and shelters.
- Camera systems with highly sensitive CCD sensors and large input lenses can work with very low light intensities and can therefore be used as night vision devices. These devices have the advantage over all other methods that they can also generate color images.
Image converter and residual light intensifier
The core of conventional night vision devices for the near infrared is an image converter tube or a residual light amplifier , in which radiation (up to 1.8 µm wavelength) hitting a photocathode on the entrance side triggers electrons, which are accelerated by a high voltage in a vacuum on the opposite side impinge on a fluorescent screen and generate a mostly greenish image there through fluorescence . Glass optics depict the surroundings on the photocathode and enable viewing of the small screens similar to binoculars or the viewfinder of a camcorder.
If there is insufficient visible light or infrared radiation for this amplification effect, an infrared lamp can illuminate the environment invisibly to the human eye.
The devices based on the image converter principle in the near infrared or through residual light amplification in the visible range are used by hunters and the military, for example. They cannot be used during the day and can be damaged by direct sunlight.
History and generations of devices
Image converter and residual light devices are divided into "generations" (see also residual light intensifier).
Generation 0 devices (infrared converters based on the near focus principle) have been known since around 1940 and were used in military vehicles as early as the Second World War . One preserved copy is in the defense technology collection Koblenz , mounted on a vehicle of the type Panzerkampfwagen V Panther .
The AEG- Telefunken 6914 is an image converter tube , as it is also installed in the Fero51 device used by the Bundeswehr .
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The Generation 1 (lifetime max 1000-2000 hours.) Works with image intensifier tubes after the inverter principle - an electron optics enables higher gain (1000-8000-fold) and image reduction. Generation 1 devices are usually supplemented with infrared lighting. Some devices from the Belarusian company Dipol come close to generation 2. Decades ago the military used a technique in which several tubes were connected in series and gave better results. However, these very bulky devices were installed almost exclusively in vehicles (e.g. tanks).
The Generation 2 (lifetime approximately 10,000-15,000 hours) also works with a microchannel plate (MCP) between the photocathode and the screen. Microchannel plates represent a secondary electron multiplier for each image point (pixel) and enable up to 20,000 times the residual light amplification.
The Generation 3 (lifetime about 15,000 hours) is to further improve this working with microchannel plate devices. The sensitive chemical gallium arsenide (GaAs) is also used here, which enables up to 50,000-fold light amplification to be achieved.
The Generation 4 is currently reserved for military use and not commercially available. Here u. a. digital signal processors are used for image processing and optimization of the image data generated by special ebCCDs .
Thermal imaging devices
Night vision devices that work on the principle of a thermal imaging camera are sensitive to the thermal radiation of the objects themselves. They work with pyroelectric or bolometer arrays (focal plane array). The devices are much more expensive and are used, for example, to search for missing people or by the military. The devices have lenses made of monocrystalline germanium and can also be used during the day.
Applications and other types
Devices of the 1st, 2nd and 3rd generation are particularly available on the civil market. They are almost exclusively hand-held devices with a monocular or binocular design that resemble binoculars . Some also have a head carrying system. The trend is towards ever smaller, lighter and more powerful (mainly in terms of battery life) devices. Since infrared radiation penetrates fog better than visible light, night vision devices or infrared cameras can also be used to advantage in poor visibility conditions.
In the military and police sector, which are driving development forward, there are a wide variety of models (manufactured depending on the application variant); This ranges from small sighting scouts, to devices attached to the head or helmet with straps, to larger night vision binoculars. In aircraft these are an integral part of the integrated equipment.
Many camcorders and digital cameras can also be used as infrared viewing devices, since the CCD or CMOS image sensor of these cameras also responds in principle to infrared radiation of up to 1.1 µm. For this there is sometimes a mode ("night shot") in which the IR cut filter, which is otherwise located in front of the chip, is swiveled away. This mode can also be used, for example, to check the functionality of infrared emitting devices (e.g. remote controls ). The test can usually be carried out with room lighting.
Near-infrared-sensitive video cameras and suitable IR spotlights are often used to monitor buildings in order to be able to observe at night without disturbing the surroundings with light.
Thermal imaging night vision devices are hardly in private use due to their high acquisition costs. They are used by the police, for border surveillance and for tracking down people and unlit vehicle columns, positions and shelters. They are often installed on board airplanes and helicopters. Even recently used paths and lanes can be recognized from the air in the dark.
A newer type of night vision device uses millimeter wave radiation instead of infrared , it can penetrate even thinner walls.
See also
literature
- Karsten Jahn: eagle owl and falcon. The development of night vision devices for the armored troops by the weapons office (army) of the German Wehrmacht . In: Klaus Christian Richter: (Ed.): Panzergrenadiers. A branch of service in the mirror of its history . Freundeskreis der Panzergrenadierruppe, Munster / Örtze 2004, ISBN 3-00-014858-2 , pp. 197-211.
