NIGHT VISION DEVICES
Night vision devices are devices that can utilize faint light sources or simple ambient light, including frequencies that are invisible to the human eye and most animals (except for rare exceptions like snakes, certain frog species, and fish). There are mainly two types of devices: the classic ones, referred to as “optoelectronic,” and the more recent “digital” ones.
THE HISTORY OF NIGHT VISION DEVICES
Night vision devices began to appear before the end of World War II, about thirty years before the first experiments with thermal vision and forty years before the creation of high-sensitivity cameras. However, their development has been slower compared to the other two technologies for two simple reasons. Firstly, this type of technology has been primarily managed by commercial manufacturers, who are more reluctant than scientists to disclose their information. Additionally, the scientific community itself favored the development of thermal vision, asserting that night vision with photocathodes was already surpassed and obsolete in the 1970s. The limited interest of the scientific community in night vision has hindered the opportunity to access many scientific studies, resulting in conflicting claims and highly subjective judgments regarding the possible superiority of one image intensifier tube over another. The purpose of this website is to clarify and address some night vision-related topics that go beyond mere advertising marketing, which can often be misleading.
For this reason, I want to inform readers in advance that night vision devices, from now on referred to by the Italian acronym “VD,” have been classified based on their technical characteristics and performance provided by the image intensifier tube, as well as the type of accompanying optics, target market, and field of use (civil, military (aviation, navy, etc.).
THE TWO MAIN TYPES OF NIGHT VISION DEVICES
These types of devices allow for the detection and collection of the faintest light sources, such as moonlight, starlight, and simple ambient light. They can also react to infrared light, which, as known, falls below the visible range of our visual system. Therefore, it can be confirmed that night vision devices are capable of capturing light that the human eye is unable to perceive.
There are two types of devices: optoelectronic and digital.
OPTOELECTRONIC NIGHT VISION DEVICE
In the case of optoelectronic night vision devices, which is the older type, the optical system consists of a lens capable of capturing the faint light reflected by subjects, as well as some light from the lower end of the infrared spectrum. This light, like all light, is composed of tiny particles called photons. The photons then pass through an image intensifier tube, which is a special vacuum electronic tube usually powered by batteries and consists of two components.
The most important component is the photocathode, which is a system that converts incoming photons from the lens into electrons (the larger the diameter of the front lens, the greater the photon beam).
The generated electrons enter the microchannel plate, which is a small glass disk composed of tiny holes that multiply the number of electrons, allowing for the amplification of the electronic signal by several thousand times.
At this point, the outgoing beam of electrons from the image intensifier tube strikes a screen coated with phosphors. The phosphors illuminate, creating a bright green image that is much brighter than what would be visually perceived solely based on the diameter of the lens.
An eyepiece within the optical system, with a focusing system, allows for the focusing of the obtained image and, in some cases, the enlargement of the image.
The images are green simply because the conversion of light photons into electrons turns the light beam into black and white. Green phosphors are used because our visual system allows for better detail perception. This is also a strategy employed in solar observations in white light or in planetary astronomical observations.
TYPES OF NIGHT VISION DEVICES
There are essentially four types of night vision devices, each of which can be further subdivided based on their technical characteristics. In terms of design, the following options are available:
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Night Vision Goggles: These provide a wide field of view, typically around 40-45 degrees, and have a single magnification. Night vision goggles are commonly used by military pilots or personnel who require excellent three-dimensional vision of the surrounding landscape. The ability to use both eyes also allows for better depth perception. Additionally, they are compact and lightweight for easy use and wear.
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Night Vision Monoculars: This group consists of devices with a wide field of view, similar to goggles, and a single magnification. They serve as a suitable compromise between night vision capabilities and enhancing human vision with higher magnifications.
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Night Vision Scopes: These devices have a narrow field of view, ranging from 4 to 15 degrees, and offer a magnification range of 3X to 10X. They are designed for precision aiming and shooting, combining night vision capability with higher magnifications.
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Night Vision Binoculars: Night vision binoculars are typically built with larger objective lenses and a focal length similar to monoculars. They also provide a medium range of magnification, from 3X to 10X. Thanks to the presence of two optical channels, they offer excellent stereoscopic vision, similar to regular binoculars.
It’s worth noting that there can be exceptions, as some devices may be convertible. For example, a night vision goggle can be transformed into a binocular by replacing the lenses, or a simple monocular can be converted into a night vision scope.
There are also further diversifications, such as night vision binoculars with a single objective lens but two eyepieces, or night vision devices that can be easily attached to rifles or mounted in front of the objective lens of telescopic sights (clip-on systems). Advanced products, especially in the military sector, allow for interchangeable lenses to increase the field of view, brightness, and focal ratio.
The initial classification of night vision devices is based on factors such as the number of objectives used, number of eyepieces, design, field of view, and intended use. However, these instruments can also be classified based on the power and characteristics of the image intensifier tube (among other factors).
GENERATIONS OF NIGHT VISION GOGGLES
As mentioned in the main features of night vision goggles, the image intensifier tube (IIT) is capable of amplifying ambient lighting conditions through the acceleration of incoming electrons. The term “generations” does not identify the viewing device itself, but rather the quality of the IIT. In practice, there may be identical devices, but of different generations due to the presence of a different IIT.
Currently, first, second, and third-generation devices are available. Like any product, there will naturally be differences regarding the baseline of a generation and its maximum expression. It is therefore useful to pay attention to verify the characteristics of each device because tools of the same generation could provide completely different detail resolution.
FIRST-GENERATION NIGHT VISION GOGGLES
First-generation night vision goggles have been on the market since the 1950s. Compared to Gen2 and Gen3, the quality of the IIT valves does not have a global standard to adhere to, and for this reason, there could be significant differences between one product and another. In general, Gen1 goggles are ideal for short-range observations, preferably during a half-moon phase or in the presence of suburban light pollution. Due to their limited effectiveness, they are always provided with an additional IR illuminator capable of increasing the clarity of perceived details, or it is advisable to purchase one separately. In this range of products, prices can range from 450 euros to approximately 800-900 euros.
SECOND-GENERATION NIGHT VISION GOGGLES
Gen2 goggles are much more performant compared to Gen1, both in terms of performance and expected lifespan. If a first-generation device is designed to provide approximately 1000 hours of usage, a second-generation image intensifier tube is guaranteed to have a usage interval between 2500 and 5000 hours. In the best-case scenario, it would be possible to use a night vision goggle for over nine years. Since these products are not used daily, it is common to purchase a Gen2 device with the awareness that it can be used well beyond ten years.
But how does a Gen2 perform so much better than a Gen1? Simply because the image intensifier tube (IIT) is optimized with a “micro-channel plate” (MCP). It is nothing more than a system of parallel electron amplifiers, thanks to the presence of a tiny glass guide containing thousands of holes. Inside it, there is a semiconductor material coating capable of producing secondary electrons. To accelerate the electrons from one side of the guide to the other, there is a coating with special metal alloys that cover the guide’s planes, maintaining a high potential difference between the top part at negative potential (cathode) and the back part at positive potential (anode).
In practice, Gen2 tubes, compared to lower-class models, offer a wider detection range, good capability to work in low-light conditions without the need for IR assistance, and show image quality much closer to that of third-generation tubes.
Even in this case, the buyer should consider that not all Gen2 devices are the same. In fact, there is a wide range of products that can be categorized into three tiers: basic, sport, and professional. Therefore, you could have Gen2 thermal goggles with the same optical characteristics, the same housing, the same buttons, but with increasingly performant image intensifier tubes, depending on the chosen model. The difference often lies in the ratio defined as LP/mm, which means “line pairs per millimeter,” representing the best resolution and image quality that can be achieved. Many standard models have a resolution between 45-50 LP/mm, while the best ones can reach 70-75 LP/mm, so the difference is significant. For this reason, I recommend readers to carefully analyze the technical specifications of a night vision goggle before making a purchase, rather than relying solely on the “Gen2” label.
THIRD-GENERATION NIGHT VISION GOGGLES
These are usually purchased by very demanding individuals, as well as by law enforcement agencies or for professional activities such as searching for missing persons. Compared to Gen2, they have a much longer lifespan, reaching up to 10,000 hours of usage, thanks to the presence of an ion barrier that extends the average life of the photocathode tubes. Additionally, thanks to the presentation of a chemical compound, they provide exceptionally sharp, contrasted, and bright images, capable of showing details invisible to lower-class products without the use of IR illuminators.
Even in this case, there are significant differences between third-generation night vision goggles. To assess their performance, the so-called FOM (Figure of Merit) is considered. It is simply the multiplication of LP/mm by the signal-to-noise ratio (often defined as SNR). An imaginary image intensifier tube with an LP/mm of 70 and an SNR of 25 would provide a FOM of 1700.
FOURTH-GENERATION NIGHT VISION GOGGLES
Its are the best that is currently available on the market. Its excellent performance is due to the absence of the IONI film – called Filmless technology, which means without film. And thanks to the presence of a self-controlled power supply (autogated). In practice, the Filmless technology and the self-controlled power supply of the intensifier tube result in the following:
- A better response of the photocathode tube, 100% better than GEN3 models.
- A better signal-to-noise ratio with excellent performance even in almost total darkness.
- A threefold increase in resolution and brightness (typically with a minimum of 64 lp/mm compared to the classic 12 lp/mm).
- A significant increase in depth of field, contrast level, and sharpness in any lighting conditions. The most noticeable difference, compared to GEN3, is in almost total darkness.
- Thanks to the self-controlled power supply of the intensifier tube, not only image resolution has improved but also the reduction of halo effect and interference from external light sources. This is a crucial factor for military and professional use, especially during nighttime operations in urban areas with dynamic lighting.
The term “GEN4” is primarily used by the United States military to describe the “filmless controlled” technology. Some of its characteristics include a resolution ranging from 64 to 72 lp/mm, a signal-to-noise ratio of 25 to 30, automatic power supply, and a minimum intensifier tube lifespan of 10,000 hours.
DIGITAL NIGHT VISION GOGGLES
In recent years, optoelectronic vision has been improved through the use of “digital imaging,” which has allowed the development of night vision systems that are not only more high-performing but also lighter, brighter, and feature-rich. For example, these systems can capture images or record short videos.
In this case, the light beam entering through the main lens is converted into a digital signal using a CMOS sensor, similar to those found in video cameras or modern mirrorless cameras. With the help of an internal electronic board and management software, the digital image is electronically enhanced and magnified multiple times. It is then sent to an LCD or OLED display for viewing. The main difference compared to optoelectronic systems is that in the former case, the incoming light beam mainly depends on the lens diameter (e.g., 40mm, 50mm, 56mm), while in the latter case, the image resolution depends on the size of the CMOS sensor used. Currently, most digital night vision goggles can display and record videos in Full HD at 1080p, with high-end models reaching resolutions of 1980p.
The use of CMOS sensors has enabled various alternative applications, such as transferring images to displays, tablets, smartphones, and digitally archiving them using memory cards, microSD cards, USB drives, and other storage devices. In some cases, it is also possible to control the functionalities of these new electronic systems via Wi-Fi, allowing image recording on a smartphone or direct streaming.
This technology is continuously evolving, thanks to ongoing improvements in CMOS sensors, management software, and high-resolution displays. If we compare the early models with those currently available, the difference in performance is significant. Now, it is even possible to obtain color images, unlike the classic green images associated with “old-school” optoelectronics.