Buying a Night Vision Device. Buyer's Guide..

Buying a night vision device. Recommendations for buyers..

Buying a night vision device. Recommendations for buyers

Source: http://nightvision.ru

Choosing and purchasing a night vision device is not an easy task, since there are currently dozens of models of night vision devices (NVD) from various manufacturers available in stores. For a non-specialist, reading the passports of all these models does not provide practically any information, especially since some domestic and foreign (mainly American) manufacturers, for advertising purposes, exaggerate the real technical characteristics of their NVDs (sometimes 5-100 times) and conduct an aggressive advertising campaign against competitors.

Without claiming to be completely complete, we hope that this guide from the manufacturer of night vision equipment, JSC Dedal-NV, will help you better understand what you want to buy.

Each NVD operates on the principle of multiple amplification of image brightness in the visible and near infrared radiation spectrum. The device consists of a lens, an image intensifier tube (IIT) with a power supply unit, and an eyepiece. Light reflected from the observed object through the lens creates an image at the input (cathode) of the IIT, which is electronically amplified and projected as a yellow-green glow on the output screen of the IIT, and then transmitted through the eyepiece to the observer's eye. Basically, the quality of the NVD is determined by the characteristics of the IIT and optics. According to the accepted terminology, image intensifier tubes are classified into three generations: I, II and III (with intermediate stages: I+, II+).

Electron-optical converter of generation I

These tubes have a glass vacuum flask with a photocathode sensitivity of 120-250 mA/lm. The light gain of these tubes is 120-900, the resolution in the center is 25-35 lines/mm.

Devices based on these image intensifier tubes can be found in a wide range of stores at prices up to $320. The distinctive feature of this type is that a clear image is observed only in the center, with distortion and lower resolution at the edges. In addition, if bright light sources, such as lanterns, illuminated windows of houses, etc., fall into the field of view, the entire image is illuminated, which prevents and even completely eliminates the possibility of observation.

Even within the same class, finished image intensifier tubes differ greatly in their parameters. Usually, after manufacturing, image intensifier tubes are sorted into groups by quality and sold at different prices. Sometimes this fact is the reason for the price difference between devices from different manufacturers. For example, our «Dedal-180» devices use converters that cost 1.5-2 times more than devices from most competing companies. The selection of image intensifier tubes for devices is mainly based on cathode sensitivity, resolution, and field of view clarity. Small black dots visible on the screen, as a rule, do not interfere with observation in the dark, and the buyer should not reject the device based on this parameter. It is better not to buy devices with bright constantly lit dots or with a light spot in the center.

You should not buy products with low image contrast. When buying a device, you can check the purity and clarity of the image yourself, but only a specialist can check the sensitivity, which is a determining parameter for night vision devices. Sensitivity can also be checked by comparing the readings of the devices in the dark.

Due to low gain, single-stage devices of the 1st generation are very critical to the luminosity of the optics and the parameters of the image intensifier tube. Only devices with high-quality image intensifier tubes, in combination with particularly high-luminosity optics (focal number no more than 1.5), can provide acceptable parameters for observation in the evening and at night with 1/4 of the moon in the sky. At lower illumination, additional infrared (IR) illumination is required. All models of the Dedal series of generation I have electronic protection against bright light, which prevents the devices from burning out during a flash of light or when turned on during the day, unlike most devices in this class.

To increase the gain of the image intensifier tube, two, three or more products are sometimes successively joined, constructively assembling them into a single housing. The gain of a three-stage image intensifier tube is 20,000-50,000. However, when joined, distortions increase greatly, and the resolution at the edges of the image field drops. Devices built on multi-stage image intensifier tubes are very bulky and heavy, so they have recently been practically replaced by small-sized devices of the I+ and II-nd generation, which have better characteristics and a similar cost.

This type of device is the next stage of development of the first generation of image intensifier tubes. At the input (sometimes at the output) instead of flat glass, a fiber-optic washer is installed, which allows to significantly increase the resolution of the image intensifier tube, reduce the distortion of the object's shape, and, in addition, protect the image from glare from side point light sources.

The characteristics of such EOPs are: light gain of about 1,000, photocathode sensitivity of min. 280 mA/lm, resolution in the center of min. 45-50 lines/mm. Devices created on the EOP of generation I+ differ from devices of the 1st generation, first of all, in a clear and comfortable picture, low level of intrinsic noise and, as a rule, a greater range in passive and active (when using IR illumination) operating modes. The devices work perfectly in urban conditions. In open areas, the devices are effective up to illumination levels corresponding to 1/4 of the moon in the sky. At lower illumination, IR illumination is required. The cost of the I+ generation image intensifier is 4-9 times higher than the I-th generation image intensifier. In this class, our company produced the Dedal-220 night vision devices and the Dedal-210 sights. Unfortunately, the manufacturer of such image intensifiers has curtailed its production program, which has led to the disappearance of devices of this class from the market.

II generation image intensifier

The II-nd generation image intensifiers differ from I+ in their design by the presence of a special electron amplifier, the microchannel plate (MCP).

Characteristics of such image intensifier tubes: light gain of about 25,000-50,000, photocathode sensitivity of min. 240 mA/lm, resolution in the center of 32-38 lines/mm. The service life of the image intensifier tube is at least 1,000-3,000 hours. There are two sizes of image intensifier tubes with 25 mm and 18 mm microchannel plates. From the observer's point of view, the larger size provides greater viewing comfort (as in large TVs), but leads to an increase in the dimensions of the device.

In this class, our company produces the multifunctional night vision device «Dedal-45» and the sight «Dedal-300». All these devices have a useful feature for the observer — manual brightness control, allowing you to select the optimal ratio of brightness gain and the level of the device's own noise for each specific observation situation and eye adaptation.

The devices of this generation do not have a boost chamber. The light gain is about 25,000-35,000, but the photocathode sensitivity reaches 600 mA/lm and is shifted to a large IR region, the resolution of the image intensifier is 39-45 lines/mm. The resource of the image intensifier is 1,000-3,000 hours. Due to the lack of a boost chamber, the image intensifiers of generation II+ have a lower brightness gain than the image intensifiers of generation II. However, due to the difference in the photocathode sensitivity of these image intensifier tubes and especially high sensitivity in the IR range, in most cases, generation II+ devices work better in open areas than generation II devices. If the main task for the NVD is night photo or video shooting, then you should choose a generation II NVD with a high brightness gain factor. Generation II and II+ devices have: automatic brightness control, protection against exceeding the overall brightness level, protection against side and direct illumination by point light sources, good image quality without distortion across the entire field of view.

These devices belong to the class of professional equipment and are currently in service in most Western countries, as they operate at very low illumination levels corresponding to the starry sky and the starry sky in light clouds.

Generation III Electron-Optical Converter

They differ from Generation II+ EOPs by a photocathode based on gallium arsenide, with an even greater shift of the photocathode sensitivity peak to the infrared region. The photocathode sensitivity reaches 900-1600 mA/lm, the EOP resolution is 32-64 lines/mm and the service life is up to 10,000 hours, which is 3 times more than the Generation II EOP. Devices based on Generation III EOPs work very well in extremely low light conditions. The picture in the device is rich, clear, with good contrast and detail elaboration. The only small drawback is the lack of protection from side light sources, since there is no fiber optic washer at the input of the image intensifier tube. In connection with this, it is not recommended to purchase devices of the third generation if you plan to work in urban conditions. The cost of devices with an image intensifier tube of the third generation is 1.5-2.5 times higher than that of devices of the second + generation and ranges from $3,000 to $13,000. Until recently, devices of the second + and third generations were used only for military purposes.

At present, several high-quality civilian devices based on II+ and III-generation EOPs are produced under the Dedal trademark.

Optics

The optical part of the NVD consists of an objective and an eyepiece. The main requirement for the objective is high light transmission in the visible and near infrared range. Numerically, it is expressed by the geometric aperture ratio (or f-number) from the series 1, 1.4, 2.0, 2.8, 4.0, etc. With an increase in the number by one stop, the lens transmits half as much light. High aperture ratio (small f-number) is very important for NVDs, especially for devices of the I and I+ generations. The deterioration of the light intensity to 2.4-2.8 results in the naked human eye seeing better than with a generation I night vision device in passive mode.

The development and production of particularly high-aperture optics with an aperture value of less than 1.5 is a complex and expensive task that not every company can afford. The cost of manufacturing high-aperture optics, of course, affects the final cost of the NVD. Many manufacturers, in pursuit of the demand of unskilled buyers to obtain high (3.5-5.0x) magnification, equip NVDs with lenses with a long focal length and low light intensity. At the same time, you need to know that if you choose a model with a higher magnification from two devices of the same generation and the same size, the image on it will be worse and the range in extreme darkness will be less than that of a device with a lower magnification and a higher light intensity.

This is especially true for hunting night sights. The peculiarity of all devices of the «Dedal» series is that, as a rule, they use only lenses with good light intensity of 1.2 or 1.5 and a lightweight design. For example, the weight of a 100 mm/1.5 lens of the «Dedal» brand is two times less than a similar lens of the Krasnogorsk plant.

Sometimes mirror-lens lenses are used for NVDs. They provide the NVD with a slightly smaller overall axial size, but have an unmasking effect and, all other things being equal, have worse light transmission. Therefore, in recent times, in Russia and abroad, mirror-lens lenses have been abandoned for NVDs.

Design

The design of the NVG eyepiece does not affect the range, but significantly affects the comfort of observation. For example, simplification of the design leads to distortion of the shape of objects and a decrease in resolution at the edge of the field of view. In addition, only part of the EOP field is visible through the eyepiece of some NVG manufacturers, but it is the EOP that is the main and most expensive element of the device. For night sights, it is very important that the eyepiece design provides a sufficient distance (at least 40 mm) from the human eye to eliminate the possibility of injury due to recoil when shooting. In the Dedal series sights, the exit pupil distance is 40-45 mm. By the way, this also determines the high quality of night photographs through the devices and scopes of the «Dedal» series.

Most Russian NVDs have high-quality glass optics. The only exceptions are very cheap first-generation NVDs, in the optics of which plastic elements are used, and some civilian NVDs from well-known American companies. The quality of such lenses is significantly worse than glass ones.

Infrared illuminator

For civilian NVDs, the presence of a built-in illuminator is an additional opportunity to illuminate the object of observation when the natural light reflected from the object is insufficient for the passive mode. Infrared illuminators are produced based on lasers, LEDs and special incandescent lamps. You should know that laser illuminators are dangerous for vision, so in most developed countries they are prohibited for domestic use. However, in Russia you can find dangerous lasers on sale.

IR LED illuminators are safe and, in addition, unlike lasers, provide a uniform luminescence field. Currently, most manufacturers have switched to IR LED illuminators with a power of 3-12 mW.

Our company equips all its devices with the most powerful infrared LED illuminator produced in Russia — 75 mW, which increases the observation range by 1.5-2 times. If your product does not have a built-in illuminator, you can buy it separately and use it autonomously.

A number of night vision devices are equipped with IR illuminators with a wavelength of 940 nm, which do not have a visible spot of IR illuminator glow. This option is recommended for law enforcement agencies, as it ensures covert observation.

Mechanical characteristics

The attractiveness of a night vision device is higher, the smaller its dimensions, weight and the greater its range. However, these parameters are in conflict with each other. A device with a larger lens provides a greater range with the same image intensifier, and the final choice is up to the buyer.

Special mention should be made of the design of night sights. It must withstand axial impact loads of up to 500 g, while the aiming mark should not move from its original position and be clearly visible under various operating conditions. A number of civilian products that have appeared on the Russian and Western markets in the last 5 years do not meet the impact strength requirements for 375 H&H and 416 Rigby calibers. They also have limitations on the possibility of installation on individual civilian weapons and have a large offset of the initial aiming point, caused by an unsuccessful design of the mechanism for inserting the mark or fastening to the gun. It should be said that there are so many design features and use of night sights that it is impossible to describe them in a short article, and we recommend that you contact our company for consultation on all issues.

Observation range

The buyer should take into account that the observation and identification range provided by night vision devices depends on the amount of natural night illumination, atmospheric transparency and the contrast between the object of observation and the background. With increased illumination, on a moonlit night in the presence of external lighting, if the object of observation is located on a light background (sand, snow), the identification range increases. In low light conditions, low atmospheric transparency, if the object of observation is located on a dark background (arable land, tree trunks, etc.), the identification range is reduced.

Below is a table of the average range of night observation and identification of a human figure on a contrasting background (according to domestic and foreign data):

Thus, before purchasing a night vision device, first of all, you need to decide which generation of devices is needed to solve your problems. The higher the generation, the higher the characteristics and capabilities of the night vision device, but the higher the cost of the product.

When choosing a night vision device, we recommend following these simple rules:

 — If you are not going to use the device for professional activities, and you do not have strict requirements for visibility at night, then you can only be guided by the appearance and cost of the model;
 — For the best quality visibility, especially in first-generation devices, choose a product with a lens with a relative aperture of at least 1.5;
 — When purchasing night vision devices, give preference to companies with extensive experience in production and sales in the external, highly competitive market. Buy models only from those manufacturers who provide warranty and post-warranty service for their devices without any problems;
 — it is best if you have the opportunity to test the product before the final purchase and compare your expectations with the capabilities of the NVD, since technical characteristics of devices are often overstated or not provided at all in passports and advertisements;
Be sure to check the functionality of the product before purchasing.

We hope that these simple tips will help you choose the right model of night vision device and experience first-hand the possibilities offered by modern high technologies!