NVD has a history of more than 40 years. These products can be divided into several generations. Every major breakthrough in the development of NVD technology will spawn a new generation of products.
The earliest generation, the earliest night vision system, developed by the US military, was applied to the Second World War and the Korean War, and these NVD systems used active infrared technology. This means that a transmitter unit called the infrared radiation source must be attached to the NVD. The unit can emit a bunch of near infrared rays, similar to those emitted by ordinary flash lamps. This beam can not be seen by the naked eye. They will be reflected from the object and then return to the lens of NVD. This system connects the anode to the cathode to accelerate the electrons. The problem with this method is that electron acceleration will distort the image and greatly reduce the life of the pipeline. The technology was first used in the military, and there was an important problem: the enemy could copy the system in a short time, which allowed enemy soldiers to use their NVD system to observe the infrared beams emitted by the equipment.
Night vision sight
The first generation of NVD abandoned active infrared technology, instead of passive infrared technology. The NVD can make use of the environmental light emitted by the moon and stars to amplify the reflected infrared rays, thus it has been called the starlight by the US Army. This means that they do not need an infrared source. This also means that when cloudy or moonless nights, their work is not very good. The first generation NVD uses the same image enhancement technology as the zeroth generation, which also accelerates the cathode and anode, so there is still a problem of image distortion and short pipeline life.
The second generation -- the significant progress of image enhancement tube technology has given birth to the second generation of NVD. They have higher resolution, better performance and better reliability than the first generation devices. The second generation's greatest achievement is that they have the ability to generate images in very weak light conditions, such as at night without a moon. Sensitivity increased because the image intensifier attached to the microchannel plate. Because MCP can increase the number of electrons instead of only accelerating the original electrons, the degree of image distortion is significantly reduced, and the brightness is also higher than that of the previous generations of NVD.
The third generation - currently the US Army adopts the third generation technology. Although there is no essential difference between the principles and the second generation, the resolution and sensitivity of this generation of NVD are better. This is because its photocathode is made of gallium arsenide, which helps improve the efficiency of photon transformation into electron. In addition, there is an ion barrier layer on the MCP, which can effectively increase the service life of the pipeline.
The night vision instrument in the film
The fourth generation, usually referred to as the fourth generation technology, is also called the "non film threshold" technology. In general, the performance of this generation system has been greatly improved in the two environments of strong and weak light.
MCP removes the ion barriers of the third generation technology, thus reducing background noise and improving SNR. The removal of ionic film can enlarge more electrons in practice, so that the distortion of the image is significantly reduced, and the brightness is obviously improved.
The introduction of the automatic threshold power supply system enables the voltage of the photocathode to be quickly connected and cut off, allowing NVD to respond instantly to the fluctuation of the luminous conditions. The progress of this technology is crucial to the NVD system, with the ability to move quickly from a strong light environment to a weak light environment (or from a weak light environment to a strong light environment), and the image does not produce any bumps. For example, imagine a movie scene that can be seen everywhere: when a spy is using a night vision eyepiece, if someone opens a nearby electric lamp, he will "lose sight". With the latest threshold power technology, changes in light conditions do not produce such a bad result, and the improved NVD system can immediately respond to changes in the light environment.
Many so-called "cheap" night vision mirrors use the zeroth generation or the first generation technology, and if you have high expectations for the sensitivity of a professional device, you may be disappointed. The second generation, the third generation and the fourth generation NVD generally have higher prices, but if they are properly maintained, they can be used for a long time. Another point is that the use of infrared radiation sources is beneficial to any NVD system in extremely dark and almost impossible to collect ambient light.
An image enhancement tube must be rigorously tested to determine whether it can meet the military standard. The standard pipe is classified as military specification (MILSPEC). Even if only one index does not conform to military standards, the pipe will be classified as COMSPEC.