AUTOMATIC BRIGHTNESS CONTROL (ABC) – An electronic circuit built into an intensifier tube that automatically reduces voltage to the microchannel plate. The ABC circuit keeps the brightness of the viewing screen within optimal limits and protects the tube by maintaining a constant maximum output level whenever the input light level exceeds a certain preset amount. The effect of ABC can be observed during rapid changes from low-light to high-light conditions when the image gets brighter and then quickly returns to a consistent level.
The automatic brightness control circuit is present in both manual gain tubes (MX-11769-type) and Aviation tubes (MX-10160-type). MX-10160 tubes utilize ABC as the sole mechanism for setting the maximum output brightness level of the intensifier tube. Similar to MX-10160 intensifier tubes, MX-11769 tubes include automatic brightness control, but also have a pigtail and variable gain circuit which allow the user to override the ABC and further reduce the maximum output brightness level with the use of a potentiometer.
AUTOGATING – Autogated tubes are equipped with a power supply that is constantly switching on and off at a very high rate, reducing the amount of voltage to the photocathode depending on the amount of ambient light. Autogating extends the operational lifetime of the tube and increases high-light performance by reducing blooming and halo intensity, while avoiding loss of resolution caused by lower cathode voltage levels.
The autogating circuit reduces the amount time the voltage is on during each oscillation, but keeps the peak voltage up which keeps the tube resolution high. Although the autogated power supply is turning off photocathode voltage for brief periods of time, the effect is not visible to the human eye and the image appears as if it were continuous.
BIOCULAR NVD – The biocular goggle has one objective lens, one image intensifier tube, and two eyepieces. The most common example is the AN/PVS-7 goggle. Here the user’s two eyes see the same two-dimensional (2D) intensified image of the scene, with no depth cues provided by binocular disparity. Goggles like the PVS-7 are well balanced and comfortable and are a good option for those who have dominant-eye issues using a monocular.
BINOCULAR NVD – The binocular goggle has two objective lenses, two image intensifier tubes, and two eyepieces. Unlike the biocular goggle, the binocular goggle creates two separate image-intensified views of the scene from two horizontally separated viewpoints. This difference between the viewpoints results in binocular disparity between the left eye and right eye images, which can provide strong cues for stereoscopic depth perception of terrain contour and other hazards.
BLACK SPOTS – These are cosmetic blemishes in the image intensifier or dirt or debris between the lenses. Black spots occur as a normal part of the manufacturing process and are acceptable as long as they do not interfere with the user’s ability to view the scene. Note: All intensifier tubes will have some spots upon close inspection.
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. 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 common in Generation 0 and 1 devices.
BRIGHT SPOTS – These defects can appear in the image area of the NVD. This condition is caused by a flaw in the film on the microchannel plate. A bright spot is a small, non-uniform, bright area that may flicker or appear constant. Bright spots usually go away when the light is blocked out and are cosmetic blemishes that are signal induced. Verify that bright spots are not simply the result of bright light in the area under observation. Bright spots are acceptable as long as they do not interfere with the user’s ability to view the scene.
BRIGHT SOURCE PROTECTION (BSP) – An electronic function that reduces the voltage to the photocathode when the night vision device is exposed to bright light sources such as room lights or car lights. BSP protects the image tube from damage and enhances its life; however, it also has the effect of lowering resolution when functioning.
BSP, as compared to ABC, reduces voltage to the photocathode rather than the microchannel plate. BSP protects the image intensifier from damage and enhances its operational lifetime, however the reduced voltage to the photocathode degrades the image by reducing resolution.
CHICKEN WIRE – An irregular pattern of dark thin lines in the field-of-view either throughout the image area or in parts of the image area. Under the worst case condition, these lines will form hexagonal or square-wave shaped lines. No action is required if this condition is present unless it interferes with the user’s ability to view an image.
COMMERCIAL SPEC – A term used to describe image tube quality, testing and inspection done by the original equipment manufacturer (OEM). In the context of image intensifier tubes, commercial spec tubes, as compared to milspec tubes, have failed to meet one or more milspec requirements. Despite not meeting all milspec requirements, modern commercial spec tubes generally have excellent performance and offer great value. A benefit to purchasing a commercial tube is that most come with a factory data sheet that states the individual cosmetic and performance specifications for each tube.
DAYLIGHT LENS COVER – Soft plastic or rubber cap with a pinhole that allows a small amount of light to enter the objective lens of a night vision device. This should be used for testing, training or demonstration purposes only, and is not recommended for an extended period of time.
DIOPTER – A unit of measure used to define eye correction. Adjustments to the diopter adjustment will provide a clearer image in each eye. Most NVD’s have a diopter adjustment to accommodate for the particular vision of each individual user. This allows a user the option to use the NVD without wearing corrective lenses.
EDGE GLOW – This is a defect in the image area of the NVD. Edge glow is a bright area (sometimes sparkling) in the outer portion of the viewing area. To check for edge glow, block out all light from the device by cupping a hand over the objective lens. If the image intensifier tube is displaying edge glow, the bright area will still be visible. Edge glow can often be caused by an emission point located outside the viewing area or improper adjustment of the internal gain potentiometers on the tube.
EMISSION POINT – A steady or fluctuating pinpoint of bright light in the image area and does not go away when all light is blocked from the objective lens of the NVD. The position of an emission point within the image area of the NVD does not move. An emission point should not be confused with a point light source in the distance.
EQUIVALENT BACKGROUND ILLUMINATION (EBI) – This is a type of noise present in an intensifier tube caused by thermionic emissions (heat) inside the tube. EBI can be observed as a yellowish haze over the image and increases as the ambient temperature increases. Tubes with high EBI will suffer from a lack of contrast and resolution, particularly in hot environments and low light conditions. EBI also determines the lowest light level at which an image can be detected. Below this light level, objects will be masked by the EBI.
FIELD OF VIEW (FOV) – The angular diameter of the image area when viewed through an optic.
FIGURE OF MERIT (FOM) – Image Intensifier tube specification designation typically used to classify which type of export restrictions apply to a particular intensifier tube. Figure of merit can be calculated by multiplying the resolution and signal-to-noise ratio of a tube. Ex. A tube with a resolution of 64lp/mm and signal-to-noise ratio of 28 would have a FOM of 1792 (64x28=1792).
FIXED-PATTERN NOISE – This is a cosmetic blemish in the image area characterized by a faint hexagonal (honeycomb) pattern throughout the viewing area that most often occurs at high light-levels or when viewing very bright lights. Fixed pattern noise is inherent in the structure of the fiber optics and can be seen in every image intensifier if the light level is high enough.
FLASHING – This is a defect in the image area of the NVD. The image appears to flicker or flash.
FLICKERING – See “flashing”
FOOTLAMBERT (fL) – A unit of brightness equal to one footcandle at a distance of one foot.
GAIN – This is the number of times a night vision device amplifies light input. Also called brightness gain or luminance gain. 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 “noisier” and the signal-to-noise ratio may go down. U.S. military Gen 3 image tubes operate at gains of between 50,000 and 80,000. 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 5,000 to 8,000. 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.
GALLIUM ARSENIDE (GaAs) – The semiconductor material used in manufacturing the Gen 3 photocathode. GaAs photocathodes have a very high photosensitivity in the spectral region of about 450 to 950 nanometers (visible and near-infrared region).
HIGH-LIGHT CUTOFF - An image intensifier protection feature incorporating a sensor, microprocessor and circuit breaker. This feature will turn the system off during periods of extreme bright light conditions.
IMAGE INTENSIFIER – An electro-optical device that detects and amplifies ambient light to produce a visual image.
INFINITY FOCUS – Adjustment of the objective lens so that a distant object, such as a star of the point light on a distant tower, forms the sharpest image.
INTERMITTENT OPERATION – This is a defect in the image area of the NVD. See “flashing”.
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 – The distance between the user’s pupils (eyeball center). The 95th percentile of US military personnel falls within the 55 to 72mm range of IPD.
IR ILLUMINATOR – Many night vision devices incorporate a built-in infrared (IR) diode that emits invisible light or the illuminator can be mounted on to 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.
IR LASER – High-power devices providing long-range illumination capability. Ranges of several thousand meters are common. Most are not eye-safe and are restricted in use. Each IR laser should be marked with a warning label like the one shown here. Consult FDA CFR Title 21 for specific details and restrictions.
IR SOURCE – This is an IR Light Emitting Diode (LED). When turned on, the IR source provides additional illumination to enhance existing light conditions used only for performing nearby tasks.
IR (INFRARED) – Area outside the visible spectrum that cannot be seen by the human eye (between 700 nanometers and 1 millimeter). The visible spectrum is between 400 and 700 nanometers.
LIGHT INTERFERENCE FILTER (LIF) – This is a light protection filter for the NVD. Use of this filter will result in a slight reduction in system gain.
LP/MM (LINE PAIRS 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. Generation 3 tubes generally have a range of 64 – 72 lp/mm, although line pair measurement does not indicate the generation of the tube. Some Generation 2+ tubes measure 28-38 lp/mm, while a Generation 1+ tube may have measure at 40 lp/mm.
LUMEN – Denotes the photons perceptible by the human eye in one second.
MICROCHANNEL PLATE – A current-multiplying optical disk that intensifies the electron image produced by the photocathode.
MONOCULAR NVD - The monocular goggle has one objective lens, one image intensifier tube, and one eyepiece. An observer who uses this device at night would see an intensified view of the scene in one eye and an unaided view in the other eye.
PHOTOCATHODE – The input optic of an image intensifier that absorbs light energy and in turn releases electrical energy in the form of an electron image.
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. While for most latest 3rd generation image intensifiers the photoresponse is in the 1800 µA/lm (2000 µA/lm for the latest Omni VI Pinnacle tubes), the actual number is more like 900 µA/lm.
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 millimeter (lp/mm) while system resolution is measured in cycles per miliradian. 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 photograph or video where the entire image resolution is important. Measured in line pairs per millimeter (lp/mm).
SCINTILLATION – A faint, random, sparkling effect throughout the image area. Scintillation is a normal characteristic of the image intensifier and should not be confused with emission points. Scintillation is more pronounced under low light conditions. Also called “video noise”.
SHADING – The viewed image should be a full circle. If shading is present, you will not see a fully circular image. Shading is indicative of a dying photocathode and is caused by a defective vacuum seal of the image intensifier. Shading is very dark and you cannot see an image through it. Shading always begins on the edge and moves inward.
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.
SYSTEM GAIN – Equal to tube gain minus losses induced by system components such as lenses, beam splitters and filters.
VARIABLE GAIN CONTROL – Allows the user to manually adjust the gain control (basically like a dim control) in varying light conditions. This feature sets the PVS-14 apart from other popular monoculars that do not offer this feature.
US Gen 3 OMNI Direct-Comparison Pics. OMNI II - OMNI VII & Filmless Under Starlight Conditions
Clear night with no moon and very little sky glow so the conditions were essentially pure starlight.
For each location and corresponding group of pictures, I used the exact same camera settings for each tube and took pictures successively using my tripod-mounted DSLR. Depending on the amount of ambient light available at each picture location, I adjusted the camera settings so the pictures would closely approximate the actual view through the monocular.