Night vision devices are residual light amplifiers which are used to observe objects at night almost as if one is observing by day. They were previously mainly employed by the military, but have also been popular for private use now for quite some time for nature observation and monitoring purposes. This type of equipment was initially difficult to afford, but by now this has radically changed so you are now able to purchase one of these devices for private purposes at low cost.
In principle, there arethree different types of night-vision devices, which differ primarily in their light outputs. There are first, second and third-generations of night vision devices.
All night-vision devices work by collecting light, via optics at the front, which is then directed to an image converter.. A photocathode captures the incoming photons (the ‘particles’ of light) and generates energy in the form of electrons from them. These electrons are greatly accelerated and shot onto a phosphor screen. This produces energy again in the form of light, free photons, which is highly amplified in comparison to before. Under no circumstances should night vision devices be used during the day, as this can cause serious damage to them.
The first generation is the simplest and also the cheapest type of night-vision device. These devices work as described previously, by increasing the intensity of residual light. In addition, they have an infrared illuminator which only needs to be used when it is completely dark. This throws out a beam of infra-red light which we cannot perceive with our eyes, which is sensitive at 550 nanometres. In contrast to the eye, night vision devices are able to register infrared wavelengths. This means that observing can be done even in absolute darkness. However, the disadvantage is that this facility cannot be used at very long distances.
These first generation devices have light amplifications of around 1000X.
The image appears green, because the blue light is shifted into the green part of the spectrum and the red is shifted into the infrared. On looking through a night vision device you will also notice noise, which appears as a constantly moving fine-grained structure. After using the device for a while, the green colour of the image will slowly fade, until the image becomes black. These first generation units usually have a service life of around 2000 hours.
Examples of 1st generation night vision devices:
The second generation works, in principle, just like the first. The difference is that the light is amplified by up to 20000X. This means that you are able to see a much greater distance with this generation. This is achieved by a micro-channel plate, which is placed behind the photocathode and has countless tubes. The electrons generated are thereby highly amplified. In addition to the much brighter image, a noticeably sharper image is also achieved.. And the range is also increased as a result of this. With the 1st generation some edge blurring is noticeable, which is virtually absent in the second generation. The second generation is also equipped with an infrared illuminator.
Most night vision devices have a magnification of around 2X or 2.5X. There are also special types with magnifications of up to 10X. Almost all these devices are very compact and are monocular, but, especially in the second generation, there are also binocular night vision devices which look like a pair of glasses. There is even a head mount with which you can use the device hands-free. These second generation units usually have a service life of around 4000 hours.
Examples of 2nd generation night vision devices:
Third generation night vision devices have a much brighter and even sharper image, than the 2nd generation. This is achieved by the use of a photocathode with the addition of the chemical gallium arsenide. The noise is thus minimized and the lifetime of the devices is higher than for the previous generations.
It is not possible to purchase third generation night vision devices in Germany. This is mainly due to patent rights regulations and that the US Government prohibits the export of this equipment.
However, there is already very good equipment from the ‘2 ½’ generation and the 2nd ‘super plus’ generation, that correspond to the quality standards of the third generation, available. . The sharpness, brightness and noise are comparable.