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What are the different grades of night vision image tubes?

Aug 17, 2023 | 08:18 pm 231 0
What are the different grades of night vision image tubes?

Vision is one of the most important senses that help us scan and process information about the environment. However, while cats, owls, wolves, and other animal kingdom representatives have been gifted by nature with the ability to see in the dark, humans are limited in these skills. 

This would not seem such a problem if humanity did not need to see in the dark occasionally. This issue was especially acute in wartime periods of history. And in general, this led to the emergence of night vision devices. But after the war ended, these devices were quickly assimilated into civilian use. Law enforcement officials use them in rescue operations, hunting, etc. 

NVDs are divided into many types and subtypes. However, some factors unite them into one general category - the principle of their operation. The focus of operation of a classic night vision device is based on converting infrared radiation created by the glow of the night sky, stars, and moon on the observed object into visible light.

The image of the observed object is projected through the lens in an inverted form onto the input glass of the electron-optical converter, a "high vacuum lamp" with two flat ends, the input and output windows, respectively. On the inside of the input window is a thin, translucent layer of light-sensitive material (photocathode) that releases electrons when light quanta are absorbed. Inside the output window is a layer of phosphor, a material that emits light when an electron hits it (the screen). The transfer of electrons emitted by the photocathode is ensured by an electrostatic field, for which a voltage of several kW is applied to the photocathode and the screen. The image obtained on the screen is viewed through an eyepiece.

The main feature that distinguishes the generation of NVDs is their main element - an electron-optical converter (EOP). The EOP is used to convert an image invisible to the human eye into a visible one and to enhance its brightness. The idea is amplified by a vacuum tube with various components. A complete night vision tube contains a photocathode, a microchannel plate, and a phosphor screen.

The generation of the device also depends on the partial or complete presence of these components in the machine and their quality.

That is, if we have a Gen2+, it stands for the following: Gen is the generation, the number "2" is the serial number of the modification, and the "+" sign indicates the presence of an intermediate or, more precisely, an improved version of the internal elements of the device. Their development can be divided into several stages, which are associated with the emergence of certain generations of NVDs. Each subsequent generation differed from the previous in terms of more extended range, better image quality, reduced weight and dimensions, longer operating time, increased resistance to light interference, and several other advantages. To date, there are three generations of NVDs. Each generation has its classification. 

It is important to note that the improvements made by these devices are determined by such characteristics as light gain, photocathode sensitivity, signal-to-noise ratio, resolution (the ability of the night vision system image intensifier to distinguish between two closely located objects. The resolution of the image intensifier is measured in pairs of lines per mm) and multiplicity.

Gen 1

This is an example of the oldest generation, dating back to the 1950s. This class's cathode sensitivity of devices is 120-250 mA/lm. The light gain of these EOPs is 120-900, and the resolution in the center is 25-35 dpi/mm. A distinctive feature of these devices is that the image is evident only in the center, with distortion and lower resolution at the edge. In addition, if bright light sources come into view, for example, streetlights, luminous windows of houses, etc., they can illuminate the entire image, hindering the ability to observe. First-generation tubes do not have any specific standard, unlike their successors, so depending on the model, they will differ. Usually, after production, they are sorted by quality into groups and sold at different prices. Sometimes this fact causes price differences between night vision devices from other manufacturers. The selection of EOPs for night vision devices is mainly based on the cathode sensitivity, resolution, and field of view purity. Tiny black dots visible on the screen, as a rule, do not interfere with observation in the dark, so they do not serve as a confirmation of a malfunction of the device or its low quality as such.

Gen 1+ is a further development of the first-generation EOP. A fiber-optic washer is installed at the entrance (sometimes at the exit) instead of flat glass, which significantly improves the tube's functionality, reduces the distortion of the object shape, and, in addition, protects the image from illumination by side spotlight sources. The characteristics of such EOPs are light gain of about 1000 and photocathode sensitivity of min. 280 mA/lm. Night vision devices based on Gen 1+ EOPs differ from Gen I night vision devices primarily by an evident and comfortable picture, low internal noise level, and, as a rule, a more extended range in passive and active (when using IR illumination) modes of operation. In open areas, night vision devices are effective up to illumination levels corresponding to 1/4 of the moon in the sky. 

The cost of this generation of devices will usually start at $350. The price will depend on the manufacturer, the quality of the material, and its form (scope, binoculars, monoculars, night vision goggles).

Gen 2

The light gain in these devices is about 25000-50000, and the photocathode's sensitivity is min. 240mA / lm, the resolution in the center is 32-35 dpi/mm. The resource of the EOP is at least 1000-30000 hours. The 2nd generation of the EOS is equipped with EOP tubes with a microchannel plate (MCP) and a multilayer photocathode with a built-in power supply. The MCP works as an electronic amplifier, is placed directly behind the photocathode, and consists of millions of short parallel glass tubes. As electrons pass through these short tubes, thousands more electrons are released. This allows 2nd generation devices to amplify light much more than 1st generation devices, providing a brighter and clearer image.

There are two EOPs sizes- 25 mm and 18 mm MCP. From the observer's point of view, the larger size provides greater viewing comfort but results in slightly larger dimensions of the night vision device.

Gen 2+, Gen 2ST, of course, will have much more advantages than the first generation. However, these are standard and traditional representatives of the second generation. It amplifies the image by about 20 thousand times. The resolution is 40-50 lp/mm. But cathode ray tubes will have lower performance than devices of the same generation but of a higher level. The service life is up to 5000 hours. 

Gen 2CGT, Gen 2MS. They have an improved resolution of 45-54 lp/mm and a signal-to-noise ratio 15/22. They have a multi-alkaline photocathode, and their shelf life is twice as long as the previous level. Given these improvements, the cost increases slightly. 

Gen 2HPT, Gen 2HP. HPT tubes are an improved version of the CGT generation tube. It is a compact multi-alkaline image intensifier of 18 mm MKP format. It increases sensitivity, resolution, signal-to-noise ratio, and modulation transfer function. These improvements provide exceptional image clarity and brightness. Most HPT specifications are generally equivalent to standard 3rd generation. HPT features a typical signal-to-noise ratio of 22 and a resolution of 64 line pairs/mm.

As for the cost of devices of this level, they can compete in price with third-generation devices, which makes it more logical to add a little money and get a device with greater autonomy.

Gen 3

Generation III EOPs differ from EOP II+ by a gallium arsenide photocathode, with an even more significant shift of the photocathode sensitivity peak to a larger infrared region and its value up to 900-1600 mA/lm. The working distance is 300 yards (275 meters), and the image gain is 30,000 to 50,000 times. An ion-barrier film was added to its structure to increase the tube's service life. Night vision devices based on the third-generation EOP work well in low-light conditions. The picture in the night vision device will be more saturated and transparent, with good contrast and detail. The only slight drawback is the lack of protection against side light sources since there is no fiber optic washer at the input of the EOP. Therefore, they are not recommended for use in urban environments.

If we are talking about Gen 3 models, they are of high quality, have a long service life, and are generally the cheapest representatives of the third generation. 

Gen 3ST is not much different from Gen 3, but according to user reviews, these tubes show images with fewer defects and "noise." 

Gen 3A represents the highest quality of the third-generation models, hand-selected to ensure this line's more productive and efficient operation. The resolution is 64-72 lp/mm. The electron-optical converters are manufactured using the same technology as the standard third-generation EOPs. However, the Gen 3A EOPs undergo additional testing, which selects the transducers with the best parameters and the lowest image noise. The service life is up to 10,000 hours.

Gen 3P/Gen 3AG. These handsets are often called Pinnacle. They are similar to Gen 3A handsets. However, they are equipped with an additional automatic power supply. Using patented Pinnacle EOPs allows you to work in environments contaminated by light sources such as city streetlights, headlights, bright flashes, etc. The Pinnacle unit reduces glare and provides a uniform, clear image. The resolution is 64-72 lp/mm, and the signal-to-noise ratio is 25/30.

Gen 3 with HS. The abbreviation HS stands for hand-selected cathode ray tubes. These tubes are more robust and transparent and have a minimum signal-to-noise ratio of 27 or higher. This level of balance characterizes how high-quality and clear the picture you will get. And this, in turn, means that the distance between you and the observed object can be significantly increased, and you will not worry about the performance and stable operation of the device.

Also, many people may need clarification on the presence of the Gen 4 designation on some models. This is still a pretty controversial issue. 

In fact, no airborne security devices meet the Gen 4 classification. The term "fourth generation of the ABI" is a marketing ploy. Indeed, initially, the updated electronic-optical transducers were called the fourth generation. However, US military quality control experts refused to define the new EOPS as Gen 4.

It turned out that these were third-generation transducers that had improved performance by removing the ion barrier film. In addition, due to the increased sensitivity, the tube's service life has significantly decreased to one thousand hours. This technology is called Filmless Gen 3 or filmless.

Such a meaningful and voluminous classification can confuse a potential user who has just started studying this issue and wants to buy such a device. 

What will your choice depend on, and what should you pay attention to? Well, first of all, you should always focus on your needs and requirements for the device, the scope of its use, and your budget. If we're talking about hunting, let's start with the fact that night hunting is prohibited in many states, and then you won't have an urgent need to buy one. However, it is an essential tool when it gets dark quite early in the fall. You may have noticed from the description of the capabilities of some generations of tubes that they are specifically rated to transmit a certain amount of light. That is, if it is not a deep night, and the light reflected from the surrounding objects is enough for the device to function, for example, Gen 2, then you do not have an urgent need to purchase the most expensive device of the Gen 3 class. Of course, if your budget is limited.

It's also important to pay attention to the shape and type of the night vision device. We have already mentioned binoculars, monoculars, glasses, and night vision sights. Their generation classification is the same. Because it only affects the principle and quality of their work. 

If we talk about military standards, it is clear that representatives of this activity prefer Gen 3 models for obvious reasons. After all, they urgently need high-quality images at a great distance from the observed object and the availability of modern additional functions, such as Wi-Fi connection, recording of observed objects, etc. Equally important is the material of the device, its weight, shockproof features, and sensitivity to environmental conditions (rain, fog, dirt, etc.). 

However, whatever generation of the device you choose to use, please pay attention to its manufacturer. For example, first-generation night vision binoculars from AGM Global Vision will be slightly more expensive than binoculars from another little-known company recently entering the market. But you can be sure of the performance of the former, as the company's name and experience guarantee the high quality of the device.

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