Buying a night vision device.
- if there are no high requirements for good visibility at night, then the choice can be made based on the appearance, taking into account the cost of the product,
- if you want to be able to see better in the NVG than with the naked adapted eye, especially if it is the 1st generation, choose from a range of products offered with lenses with a relative aperture of at least 1.5,
- select the manufacturer. Give preference to companies with extensive experience in the production of NVG and their sales in the external, highly competitive market. You should buy products 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 in passports and advertising,
- check the functionality of the product and, if everything is in order,
Buying a night vision device (some recommendations for the buyer) or
«Looking into the darkness. Night vision devices»
Magazine «Gun. Weapons and ammunition.» 4/1998
Introduction
This is not an easy task (!), since dozens of models of night vision devices (NVD) from various manufacturers are currently available in stores, and reading the data sheets of these devices provides virtually no information for a non-specialist in this field. This is even more difficult since some domestic and foreign (mainly American) NVD manufacturers exaggerate (by 5-100 times) the actual technical characteristics of their NVDs for advertising purposes and conduct an aggressive advertising campaign against competing Russian NVDs. 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 electron-optical converter (EOC) with a power supply and an eyepiece. Light reflected from the object of observation through the lens creates an image at the input (cathode) of the EOC, which is electronically amplified and projected in a yellow-green glow on the output screen of the converter, then transmitted through the eyepiece to the observer's eye.
Basically, the quality of the NVD is determined by the characteristics of the EOC and optics.
According to the terminology accepted in the world, image intensifier tubes are classified into three generations — I, II and III (with some intermediate stages I+, II+).
Electron-optical converter
Generation I
The EOPs have a glass vacuum flask with a photocathode sensitivity of 120-250 mA/lm. The light gain of these EOPs is 120-900, the resolution in the center is 25-35 lines/mm. You can find a wide variety of devices with these EOPs in stores (priced up to $320). The distinctive feature of these devices is that the image is clear only in the center, with distortion and lower resolution at the edge. In addition, if bright light sources fall into the field of view, such as lanterns, illuminated windows of houses, etc., they can illuminate the entire image, preventing observation. Even in the same class, finished EOPs differ greatly in their parameters from each other. Usually, after production, they 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-Handy and Dedal-140 devices use an image intensifier tube 1.5-2 times more expensive than those from most competing companies/. The selection of image intensifier tubes for devices is mainly based on the cathode sensitivity, resolution, and field of view clarity. Small black dots visible on the screen usually 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 at a test bench or by comparing devices in the dark, and this parameter is decisive for night vision devices. Due to the low gain, single-stage devices of the 1st generation are very critical to the optics aperture and image intensifier tube parameters. Only devices with selected image intensifiers, in combination with particularly high-aperture optics (focal number no more than 1.5), can provide acceptable parameters for observation in the evening and at night in the presence of the 14th moon in the sky. In lower light conditions, additional infrared (IR) illumination is required. All devices of the Dedal Generation I series 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.
Multi-stage image intensifiers of generation I
To increase the gain of the image intensifier tube, two, three or more products are sometimes joined in series, constructively assembling them into one 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 similar cost.
Generation I + (Super I + in foreign literature)
This is a further development of the first generation EOP. At the input (sometimes at the output) a fiber-optic washer is installed instead of flat glass, which allows to significantly increase the resolution of the EOP, reduce the distortion of the object shape and, in addition, protect the image from illumination by side point light sources. The characteristics of such EOPs are: light gain of about 1000, photocathode sensitivity of min. 280 mA/lm, resolution in the center of min. 45 lines/mm. Devices built on the I+ generation EOP differ from the devices of the first generation, first of all, in a very 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 great in urban conditions. In open areas, the devices are effective up to illumination levels corresponding to 14 moons in the sky. At lower illumination, IR illumination is required. The cost of the EOP is 4-9 times higher than the EOP of the 1st generation.
In this class, our company produces night vision devices Dedal-220 and sights Dedal-200.
Generation II.
Structurally, the 2nd generation EOP differs from the I+ by the presence of a special electron amplifier — a microchannel plate (MCP). The characteristics of such EOPs are light gain of about 25,000-50,000, photocathode sensitivity of at least 240 mA/lm, resolution in the center of 32-35 lines/mm. The EOP resource is at least 1000-3000 hours. There are two sizes of EOPs — with MCP 25 mm and 18 mm. From the observer's point of view, a larger size provides greater comfort of observation (like a large TV), but also leads to slightly larger dimensions of the device. In this class, our company produces a multifunctional night vision device Dedal-41 and sights Dedal-40, 40m, 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.
Generation II.+(sometimes in the literature as generation II)
There is no acceleration 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 on the image intensifier is 39-45 lines/mm. The resource of the image intensifier is 1000-3000 hours. Due to the lack of an acceleration chamber, generation II + image intensifiers have a lower brightness gain factor than generation II image intensifiers. However, due to the difference in the photocathode sensitivity of these image intensifiers and especially high sensitivity in the IR range, in most cases, generation II + devices can be seen in open areas better than generation II. If the main task for the NVD is night photography or video shooting, then you should choose a generation II NVD with a high brightness gain factor. Generation II, 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 still 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.
They differ from the II+ generation EOPs by a gallium arsenide-based photocathode, with an even greater shift in the photocathode sensitivity peak to a larger IR region and its value up to 900-1600 mA/lm, a resolution of 32-64 lines/mm on the EOP and a service life of up to 10,000 hours, which is 3 times more than the II-generation EOPs. Devices based on the III-generation 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 EOP input. In this regard, it is not recommended to purchase III-generation devices if you plan to work in urban conditions. The cost of the III-rd generation EOP devices is 1.5-2.5 times higher than the II+ generation and ranges from 3,000 to 7,000 US dollars. Until recently, II+ and III-rd generation devices were used only for military purposes. Currently, several high-quality civilian devices based on II+ and III-rd 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 IR 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 step, the lens transmits half as much light. High aperture ratio (small f-number) is very important for NVDs, especially for 1st 1+ generation devices. Deterioration of aperture ratio to 2.4-2.8 results in the naked eye seeing better than with first-generation NVDs in passive mode. Development and production of particularly high-aperture optics with an f-number less than 1.5 is a complex and expensive task that not every company can handle. The cost of manufacturing high-aperture optics, of course, affects the final cost of the NVD. Many manufacturers, in pursuit of demand from unqualified buyers, equip NVDs with lenses with a long focal length and low light intensity to obtain high (3.5-5.0 times) magnification on NVDs. At the same time, you need to know that if you give preference to a device with high magnification among two devices of the same generation and the same size, then you will see worse (!) in it and the range in extreme darkness will be less than with a device with lower magnification and higher light intensity. This is especially true for hunting night sights. A feature of all Dedal series devices is that, as a rule, only lenses with good light intensity of 1.2 or 1.5 and lightweight design are used. For example, the weight of a 100mm/1.5 Dedal lens is two times less than a similar lens from 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, recently in Russia and abroad, they have refused to use mirror-lens lenses for NVDs. The design of the NVD 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 a part of the EOP field is visible through the eyepiece of some NVD manufacturers, and the EOP is so expensive. For night sights (very important!), the eyepiece design must ensure sufficient removal (at least 40 mm) of the human eye when shooting, excluding the possibility of its damage due to recoil. In Dedal series sights, the exit pupil distance is 40-45 mm. By the way, this also determines the high quality of night photographs through Dedal series devices and sights. Ask other companies to show their photographs! 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 of observation may not be enough for the passive mode. IR illuminators are produced on the basis of lasers, LEDs and special incandescent lamps. It should be known that laser illuminators are dangerous for vision, therefore in most developed countries they are prohibited for domestic use. In Russia, you can find dangerous lasers on sale. Illuminators based on IR LEDs are safe and, in addition, unlike a laser, provide a uniform glow field. At the moment, most manufacturers have switched to diode IR illuminators with a power of 3-12 mW. Our company equips all its devices with the most powerful IR LED illuminator produced in Russia — 35 mW, which provides a 1.5-2 times greater observation range. If your product does not have a built-in light, you can buy it separately and use it autonomously.
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 objective lens provides a greater range with the same EOP, and the final choice is up to the buyer. Particular attention should be paid to 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 resistance requirements, 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 mounting on the gun. It should be said that there are so many features of the design and use of night sights that they cannot be described in a short article, and we recommend that you contact our company with your questions for a consultation (free). In any case, when buying a sight, preference should be given to the company that can prove to you the reliability and efficiency of its products.
SUMMARY
Thus, before buying 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. Further, we recommend that you follow the following rules when choosing: