• Autogating: When the power supply is “auto-gated,” it means the system is turning itself on and off at a very rapid rate. This is done to reduce the amount of light reaching the photocathode and thus maintains a higher-quality image during high light and variable lighting environments. Without autogating, there will be image degradation, and the photocathode will become overwhelmed with light, resulting in what users refer to as “blooming,” where subjects and targets around the periphery of the light source become difficult to see.  
  • Automatic Brightness Control (Auto-Gain): An electronic feature that automatically reduces voltages to the microchannel plate to keep the image intensifier’s brightness within optimal limits and protect the tube. The effect of this can be seen when rapidly changing from low-light to high-light conditions; the image gets brighter and then, after a momentary delay, suddenly dims to a constant level. 
  • Binocular: A system where there are 2 objective and 2 ocular lenses, in which each eye observes a separate optical component. RNVGs are an example of a Binocular device. 
  • Black Spots/Dark Spots (AKA: “Blems”): There are typically two types of dark spots – factory dark spots and user-induced dark spots (aka “Blems”). Due to the sensitive nature of the manufacturing process, sometimes debris and other particles can become trapped inside the intensifier and present themselves as factory dark spots. Typically, factory dark spots are more “fuzzy” in nature and sometimes have a slightly lighter ring around them. User-induced blemishes are typically not circular in nature and are often induced by high light sources such as high-power lasers or lights. Finally, other blemishes can be caused by debris inside the housing sitting on top of the output screen, which is caused by improper assembly or a previously-stuck piece of debris that has fallen onto the output screen due to vibration or shock to the night vision device. For more details on factory dark spots and blemishes, see our BLOG article HERE.
  • Blooming: Loss of the entire night vision image, parts of it, or small parts of it, due to intensifier tube overloading by a bright light source. Also, known as a “halo” effect, the viewer sees a “halo” effect around visible light sources. When such a bright light source comes into the night vision device’s view, the entire night vision scene, or parts of it, becomes much brighter, “whiting out” objects within the field of view. Blooming is a common side-effect of using high-powered IR lasers as close distances. 
  • Diopter: Generally, the adjustable housing in which the ocular or “eyepeice” lens is housed. Also the unit of measure used to define eye correction or the refractive power of a lens. Usually, adjustments to an optical eyepiece accommodate for differences in individual eyesight. Most systems provide a +2 to -6 diopter range, with most users finding -0.5 being the most comfortable/natural for use.
  • Distortion: There are two types of distortion found in night vision systems. One type is caused by the design of the optics, or image intensifier tube, and is classical optical distortion. The other type is associated with manufacturing flaws in the fiber optics used in the image intensifier tube.
  • Emission Point: A steady or fluctuating pinpoint of bright light in the image area that does not go away when all light is blocked from the objective lens. The position of an emission point within the field of view will not move. If an emission point disappears or is only faintly visible when viewing under brighter nighttime conditions, it is not indicative of a problem. If the emission point remains bright under all lighting conditions, the system needs to be repaired. Do not confuse an emission point with a point of light source in the scene being viewed.
  • Equivalent Background Illumination (EBI): This is the amount of light you see through a night vision device when an image tube is turned on, but no light is on the photocathode. EBI is affected by temperature; the warmer the night vision device, the brighter the background illumination. EBI is measured in lumens per square centimeter (lm/cm2). The lower the value, the better. The EBI level determines the lowest light level at which an image can be detected. Below this light level, objects will be masked by the EBI.
  • Eye Relief: The distance a person’s eyes must be from the last element of an eyepiece in order to achieve the optimal image area. Milspec eye relief is 25mm, but most users will find that distance to be quite close, and 35mm is a more acceptable eye relief for comfortable use with common ballistic eye protection (eg, Oakley M-Frames).
  • Field of View (FOV): The diameter of the imaged area when viewed through an optic. Usually measured in Degrees.
  • Figure of Merit (FOM): A general measurement of tube performance, calculated on resolution (lp/mm) multiplied by the signal-to-noise ratio. For more information, see our short article HERE.
  • Fixed Pattern Noise: A faint hexagonal (honeycomb) pattern sometimes referred to as “Chickenwire”, seen throughout the image area that most often occurs under high-light conditions. This pattern is inherent in the structure of the microchannel plate and can be seen in virtually all GEN2  and GEN3 systems if the light level is high enough.
  • Gain: Also called brightness gain or luminance gain. This is the number of times a night vision device amplifies light input. It is usually measured as tube gain and system gain. Tube gain is measured as the light output (in fL) divided by the light input (in fc). This figure is usually expressed in values of tens of thousands. If tube gain is pushed too high, the tube will be “noiser.” U.S. military GEN3 image tubes operate at gains of between 20,000 and 45,000. On the other hand, system gain is measured as the light output (fL) divided by the light input (also fL) and is what the user actually sees. System gain is usually seen in the thousands. U.S. military systems operate at 3,000 to 13,000. In any night vision system, the tube gain is reduced by the system’s lenses and is affected by the quality of the optics or any filters. Therefore, system gain is a more important measurement to the user, with the primary contributing factor of system gain being the intensifier. Higher system gain caused by substituting lenses may not always mean better performance, as it does not measure the amount of refraction. As an example, some lightweight lens systems will give a higher system gain number, but this is caused by fewer anti-glare coatings.
  • Gallium Arsenide (GaAs): The semiconductor material used in manufacturing the GEN3 photocathode. GaAs photocathodes have a very high photosensitivity in the spectral region of about 450 to 950 nanometers (visible and near-infrared region). GEN2+ tubes do not use GaAs photocathodes, and have a higher photosensitibity in the spectral region of 325-875 nanometers. This is another example of the “trade-offs” differentiating GEN2+ versus GEN3, as opposed to one being simply “BETTER” than the other. 
  • Generations or “GEN”: To date, there have been four Generations of Image Intensifications devices; GEN1, GEN2, GEN2+. and GEN3. Developmental laboratory work is ongoing, and the U.S. military may designate loosely use the term “GEN4” to describe emerging technologies or combinations of technologies. However, no definition for GEN 4 presently exists.  These are the generations, from oldest to newest:
    • GEN1 – The “starlight scopes” developed during the early 1960’s for use in Vietnam were the first Generation of image intensifier devices. In GEN1 night vision units, three image intensifiers were connected in a series, making the units longer and heavier than later night vision. GEN1 equipment produced an image that was clear in the center of the field of view but suffered from large optical distortion around the periphery, and had a limited photomultiplier effect. GEN1 equipment was also subject to severe “blooming”.
    • GEN2 – The development of the microchannel plate, or MCP, in the late 1960s brought on the second Generation of Image Intensification night vision. The MCP accelerated and multiplied electrons, which provided the gain previously supplied by coupling three image intensifiers together (GEN1), significantly reducing the size and weight of the system. This allowed for the design of smaller night vision goggles and hand-held devices. The MCP also provided much more robust operation when bright lights entered the field of view. GEN2 tubes still used the same tri-alkali photocathode as the GEN1 devices and, while a major improvement in form factor, weight and application, still had very poor performance compared to later generations.
    • GEN3 – Third-Generation image intensifiers were developed in the mid-1970s and became widely available during the 1980s. GEN 3 introduced two major technological improvements: the gallium arsenide (GaAs) photocathode and the ion barrier film to the microchannel plate. The GaAs photocathode radically increased the tube’s sensitivity to light compared to the Tri-Alkali photocatodes in GEN2 devices,especially in the near-infrared range of the spectrum. It also enables GEN3 devices to function at greater detection distances, and improves system performance under very low-light conditions. Application of a metal-oxide ion barrier to the MCP increases the life of the image tube (See “Thin-Film” and “Unfilmed”). 
    • GEN2+ Yes, GEN2+ is not only much “newer” technology than GEN3, but has undergone continuous improvement since being introduced. GEN2+ tubes use neither Gallium Arsenide MCPs, nor the older tri-alkali types of the much older GEN2. Using ALD (Atomic Layer Deposition), modern GEN2+ tubes coat the MCP substrate with Magnesium Oxide and/or Aluminum Oxide, which not only decouple the secondary electron emissions properties from the substrate, but also allow a much higher secondary electron yield than older technologies. The inner walls of the system on the newest GEN2+ tubes are also coated with alkali halides to further enhance electron cascade. While this is a an overall different method to achieve the photomultiplier effect, with its own inherent strengths and weaknesses,current GEN2+ technology rival and in some cases surpass the performance of GEN3 systems. 
  • I2 (Image intensification): Collects and intensifies the available light in the visible and near-infrared spectrum. Offers a clear, distinguishable image under low-light conditions.
  • ION-BARRIER or “FILM”: This film is an ultra-thin layer of material, typically sintered aluminum oxide, deposited on the input surface of the microchannel plate (MCP). Its purpose is to “catch” ionized particles, which can be harmful to the rest of the system over long periods of use. Elbit tubes are marketed as being “thin-film,” and L3Harris tubes are marketed as being “unfilmed”, presumably to promote the idea that more light is being allowed to pass through and produce a better image. The jury is still out on this, and whether there is a trade-off between being “unfilmed” and having a shorter system life. 
  • Interpupillary adjustment: The distance between the user’s eyes (pupils) and the adjustment of binocular optics to adjust for differences in individuals. Improperly adjusted binoculars will display a scene that appears egg-shaped or as a reclining figure-8.
  • Interpupillary Distance (IPD): The distance between the user’s pupils (eyeball centres). The 95th percentile of people falls within the 55 to 72mm range of IPD.
  • Infrared Light: Area outside the visible spectrum that cannot be seen by the human eye (between 700 nanometers and 1 millimetre). The visible spectrum is between 400 and 700 nanometers.
  • IR Illuminator: Many night vision devices incorporate a built-in infrared (IR) diode that emits invisible light, or the illuminator can be mounted onto it as a separate component. IR light cannot be seen by the unaided eye; therefore, a night vision device is necessary to see this light. IR Illuminators provide supplemental infrared illumination of an appropriate wavelength, typically in a range of wavelengths (e.g., 730nm, 830nm, 920nm), and eliminate the variability of available ambient light, but also allow the observer to illuminate only specific areas of interest while eliminating shadows and enhancing image contrast. “Full Power” or “Restricted” IR Laser devices designed for military & law enforcement use can provide very long-range illumination capability. Ranges of several thousand meters are common. These units are not eye-safe and are restricted in use. Consult the FDA CFR Title 21 for specific details and restrictions.
  • Lp/mm (Line pair per millimeter): Units used to measure image intensifier resolution. Usually determined from a 1951 U.S. Air Force Resolving Power Test Target. The target is a series of different-sized patterns composed of three horizontal and three vertical lines. A user must be able to distinguish all the horizontal and vertical lines and the spaces between them. Typically, the higher the line pair, the better the image resolution.
  • Lumen: Denotes the photons perceptible by the human eye in one second.
  • MCP (Microchannel Plate): A Microchannel Plate (MCP) is a crucial component in image intensifier tubes (the “heart” of night vision devices) and various scientific detectors. It is a thin, disc-shaped slab, typically made of resistive lead glass, that functions as a high-speed, high-gain electron multiplier. Electrons fed to the MCP by the PHOTOCATHODE are multiplied in number exponentially, and passed on to the PHOSPHOR SCREEEN. A MCP is found only in GEN2, GEN2+, or GEN3 systems. MCPs eliminate the distortion characteristic of GEN 1 systems. The number of holes (channels) in an MCP is a major factor in determining resolution. 
  • Monocular: A single-channel optical device. Such as a PVS-14
  • Near Infrared (NIR): The shortest wavelengths of the infrared region, nominally 750 to 2,500 nanometers.
  • PHOSPHOR SCREEN: The phosphor screen in an intensifier tube is a complicated micro-sandwich of phosphorescent chemicals and substrates, which becomes electrostatically excited when hit with electrons exiting the MCP. The screen converts a wide spectrum of light into the visible spectrum and passes that image to the output lens
  • Photocathode: The Intensifier Tube component that is responsible for converting incoming photons (light particles) into electrons through the photoelectric effect. These electrons then pass to the MCP. The type of material used in this component is a distinguishing characteristic between GEN2+ and GEN3 tubes
  • Photocathode Sensitivity: Photocathode sensitivity is a measure of how well the image intensifier tube converts light into an electronic signal so it can be amplified. The measuring units of photocathode sensitivity are micro-amps/lumen (µA/lm) or microamperes per lumen. This criterion specifies the number of electrons released by the Photocathode (PC). PC response is always measured in isolation with no amplification stage or ion barrier (film). Therefore, tube data sheets (which always carry this “raw” figure) do not reflect the fact that over 50% of those electrons are lost in the ion barrier. 
  • Resolution: The ability of an image intensifier or night vision system to distinguish between objects close together. Image intensifier resolution is measured in line pairs per millimetre (lp/mm) while system resolution is measured in cycles per milliradian. For any particular night vision system, the image intensifier resolution will remain constant, while the system resolution can be affected by altering the objective or eyepiece optics by adding magnification or relay lenses. Often, the resolution in the same night vision device is very different when measured at the centre of the image and at the periphery of the image. This is especially important for devices selected for photographing or video where the entire image resolution is important. Measured in line pairs per millimetre (lp/mm).
  • Phosphor Screen: The image tube output that produces the viewable image. Phosphor (P) is used on the inside surface of the screen to produce the glow, thus producing the picture. Different phosphors are used in image intensifier tubes, depending on the manufacturer and tube Generation.
  • Signal to Noise Ratio (SNR): A measure of the light signal reaching the eye divided by the perceived noise as seen by the eye. A tube’s SNR determines the low-light resolution of the image tube; therefore, the higher the SNR, the better the ability of the tube to resolve objects with good contrast under low-light conditions. Because SNR is directly related to the photocathode’s sensitivity and also accounts for phosphor efficiency and MCP operating voltage, it is the best single indicator of an image intensifier’s performance. Scintillation, also known as electronic noise; a faint, random, sparkling effect throughout the image area. Scintillation is a normal characteristic of microchannel plate image intensifiers and is more pronounced under low-light-level conditions.
  • System Gain: Equal to tube gain minus losses induced by system components such as lenses, beam splitters, and filters.
  • Variable or “Manual” Gain Control: Allows the user to manually adjust the gain control (basically like dimming a light) in varying light conditions. PVS-14s, the AEON ANVB and others have this feature. It’s important to note that, for manual gain to function, Type 11769 tubes must be used. Type 10160 tubes are incompatible with Manual Gain.