faqs
1. Auto-Gating
Auto-Gating is the electronic solution that reduces the duty cycle of the cathode voltage by rapidly switching the voltage on and off. It is a proprietary means to preserve the high MTF (Modulation Transfer Function) and resolution that is obtained at the full operating voltage while reducing the strain of high illumination levels on the image intensifier tube. This is done by reducing the average current coming from the photocathode. Auto-Gating constantly operates to improve the quality of the image, not only during day-night-day transition, but also under dynamic lighting conditions such as military operations in urban terrain which define many of today's missions. Auto-Gating is standard on XR5™ and optional on XD-4™ Image Intensifier Tubes.
2. Black Spots - BlemishesCosmetic blemishes in the image intensifier or dirt/debris between the lenses. Black spots in the image intensifier do not affect the performance or reliability of the device and are inherent in the manufacturing processes
3. Brightness Gain -When referring to an image intensification tube, brightness gain is the ratio of the brightness of the output in units of lm/cm2
4. 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, BSP may have the effect of lowering resolution when it is functioning
5. Bright Spots.These are signal- induced blemishes in the image area caused by a flaw in the film on the MCP. A bright spot is small, non- uniform, bright area that may flicker or appear constant. Bright spots usually go away when the light is blocked out. Not all bright spots make the ANVIS unserviceable. A test can be performed as follows: Place a cupped hand over the lens to block out all light. Make sure any bright spot is not simply a bright area in the viewed scene. If the bright spot remains, an emission point exists and needs to be checked.
6. Collimation -The act of making rays of light travel in parallel lines. Also the process of aligning the various internal optical axes of a system with each other.
7. Convergence -The shifting of an observer's eyes inward to view a nearby object i.e. crossing the eyes.
8. Chicken Wire -An irregular pattern of dark lines in the image area or in parts of the image area. Under the worse condition, these lines will form hexagonal or square-wave shaped lines.
9. Distortion -Three types of distortion are most significant to night vision devices: geometric, "S" and sheer. Geometric Distortion - is inherent in all Gen 0 (infrared Tubes ie. B-20) and Gen I image intensifiers and in some Gen II image intensifiers that use electrostatic rather than fibre-optic inversion of the image. Geometric distortion is eliminated in image tubes that use a microchannel plate and fibre-optics for image inversion, however, some S-distortion can occur in these tubes. S-Distortion - results from the twisting operation in manufacturing fibre-optic inserters ). Usually S-Distortion is very small and is difficult to detect with the unaided eye. Sheer Distortion - can occur in any image tube that uses fibre-optic bundles for the phosphor screen. It appears as a cleavage or dislocation in a straight line viewed in the image area as through the line were sheered.
10. Electronic Noise -Also known as Scintillation. 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.
11. Equivalent Background Illumination (EBI) -This is the amount you see in an image tube that is turned on but there is no light at all on the photocathode; it is affected by temperature where the warmer night-vision device, the brighter the background illumination. EBI is measured in lumens per square centimetre (lm/cm2) wherein the lower the value the better. The EBI level determines the lowest light level at which you can detect something. Below this light level, objects will be masked by the EBI.
12. Fiber Optic Inverter -A bundle of microscopic light transmitting fibers twisted 180 degrees.
13. Field-of-View (FOV) -The width or spatial angle of the outside scene that can be viewed through the intensifier tubes measured laterally and vertically. Typical NVGs have a 40° FOV. There are NVGs in development that attempt to increase this FOV significantly in an effort to enhance pilot performance. An example of a wide FOV NVG would be the Panoramic NVGs'.
14. Figure of Merit (FOM) -Image Intensification tube specification designation, calculated on line pair per mm X signal to noise. The US government applies FOM as a method of controlling Image Intensified equipment.
15. Fixed Pattern Noise (FPN)A faint hexagonal (honeycomb) pattern 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 Gen II and Gen III systems if the light level is high enough.
16. Gain -Also called brightness gain or luminance gain. This is the number of times an image intensifier tube amplifies light input. It is usually measured as tube gain and system gain. 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.
17. Gallium Arsenide (GaAs) -The semiconductor material used in manufacturing of the Gen III photocathode.
18. Generations of Image Intensifiers -Image intensifier tubes are classed by generation (GEN) numbers assigned by the US Army's Night Vision Laboratory. Each GEN denotes a new contract or manufacturing process. Note: Generations do not define the performance specs of the image intensifier.
Generation I
It started with electrostatically focused Generation I tubes featuring high image resolution, a wide dynamic range and low noise
Generation II
Introduced the Micro Channel Plate for much higher gain in the 1980´s. The original image resolution was less than that of the first generation intensifiers but the gain was much higher.
Generation III
In the late 1980´s an Image Intensifier with a GaAs photocathode was developed showing an enhanced sensitivity in the Near-Infrared. In the late 1990´s Gen III tubes with greatly improved performance appeared on the market. These types are called Gen III Omni III and Gen III Omni IV.
This condition may exist when there is a difference in brightness between the two image intensifier assemblies within the same binocular.
20. Image Distortion -This problem is more easily detected in high- light conditions. Image distortion is evidenced by vertical objects, such as trees or poles appearing to wave or bend when the user moves his head vertically or horizontally when looking through the goggles. Ground surfaces in the direction of hover may appear to swell or sink. Distortion does not change during life of an image intensifier. Limits on allowable distortion are an important part of performance specifications since excess distortion can interfere with viewing the image and thus with the operator ability to perform necessary flight maneuvers.
21. Line Pairs per Millimetre (lp/mm) -Units used to measure image intensifier resolution. Usually determined from a 1951 Air Force Resolving Power test target. The target is a series of different sized patterns composed of three horizontal and three vertical lines. The lines and spacing between lines in each of the different patterns differ in width; the narrower the width, the greater the resolution is needed to distinguish the lines in a given pattern. Human test subjects must be able to clearly distinguish all the horizontal and vertical lines of a particular pattern in order for an image intensifier to achieve the resolution represented by that pattern.
22. Lumen -The semiconductor material used in manufacturing of the Gen III photocathode.
23. LuxA unit measurement of illumination. The illuminance produced on a surface that is on meter square, from a uniform point source of one-candela intensity, or one lumen per square meter.
24. Magnification -The magnifying power of the lens. Four power (4X) indicates that the image will appear four times larger than if viewed with a 1X lens.
25. Microamps per lumen -The measure of electrical current (A) produced by a photocathode when it is exposed to a measured amount of light (lumens).
26. Microchannel Plate (MCP) -A metal coated glass disk that multiplies the electrons produced by the photocathode. PHOTONIS SAS produces MCP's with 11 million pores and is constantly developing and improving the performance of the MCP for enhanced image intensifier tube performance. Electrons entering the channel strike a wall and knock off additional electrons which in turn knock off more electrons, producing a cascading effect. MCPs eliminate the distortion characteristic of GEN I systems. The number of holes in an MCP is a major factor in determining resolution.
27. MILSPEC -Term for Military Specification. It is the minimum acceptable requirements for products procured by the US Department of Defence. Use of the term MILSPEC indicates that the product meets applicable military specifications.
28. Near-Infrared -The shortest wavelengths of the infrared region, normally 750 to 2,500 nanometers (nm). GEN II operates from around 440 to 950 nanometers.
29. Output Brightness Variation -This condition is evidenced by areas of varying brightness in or across the image area. The lower contrasts do not exhibit distinct lines of demarcation nor do they degrade image quality. This condition should not be confused with shading.
30. Phosphor Screen -The phosphor screen converts electrons into photons. A very thin layer of phosphor is applied to the output fiber optic system, and emits light when struck by electrons. See also Photocathode.
31. Photocathode -The input surface of an image intensifier that absorbs light energy and in turn releases electrical energy in the form of an electron image. The type of material used is a distinguishing characteristic of the generations of image intensifiers.
32. Photoresponse (PR) -See Photosensitivity
33. Photosensitivity (Photoresponse) -Also called photocathode sensitivity or photoresponse. The ability of the photocathode material to produce an electrical response when subjected to light waves (photons). Usually measured in microamps of current per lumen (mA/lm).
34. 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 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 millimetre (lp/mm).
35. RMA -Range Migration Algorithm
36. 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.
37. 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
38. 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 manufacturer and tube generation.
39. System Gain-Equal to tube gain minus losses induced by system components such as lenses, beam splitters and filters.
40. Thermal Imaging-All objects, natural and manmade, emit infrared energy as heat. By detecting very subtle temperature difference of everything in view, infrared (or thermal imaging) technology reveals what otherwise would be invisible to the naked eye. A thermal imaging device uses a special lens that focuses infrared light into an array of infrared detector elements. The detector elements create detailed temperature pattern called a thermogram which is translated into electric pulses. The impulses are sent to a signal processing unit, a circuit board with dedicated chip that sends the info through an electronic display component. The resulting image will appear in various colors depending on the intensity of the infrared emission.
41. NETD (Noise Equivalent Temperature Difference) -Thermal Sensitivity or small temperature difference that thermal imaging camera can detect. Lesser the better.
42. NUC (Non Uniformity Correction)Each pixel of the matrix has the ability to generate a signal different from the signals of other elements under the same conditions of observation. This non-uniformity leads to the appearance of geometric noise in the picture. This effect is pronounced in the non-cooled system. Hence it is necessary to periodically perform a non-uniformity correction during the operation of the sight.
43. Polarity (White Hot/Black Hot)Warm objects appear in dark tones, cool in white/ Cool objects appear in white tones, warm in white. Also called as Image Inversion.
44. Anti Reflex Coating-Type of optical coating applied to the surface of lenses and other optical devices to reduce reflection. This improves the efficiency of the system since less light is lost.
45. LWIR (8-15µm)-This is the "thermal imaging" region, in which sensors can obtain a completely passive picture of the outside world based on thermal emissions only and requiring no external light or thermal source such as the sun, moon or infrared illuminator. Forward-looking infrared (FLIR) systems use this area of the spectrum. This region is also called the "thermal infrared."The operating distance, indoor-outdoor operation, temperature and emissivity of the bodies of interest. For instance, long wavelengths (LWIR) are preferred for outdoor operation since they are less affected by radiation from the Sun. LWIR cameras are typically uncooled systems using a microbolometer Focal Plane Arrays commonly used in industrial IR applications, although cooled LWIR cameras using Mercury Cadmium Tellurium (MCT) detectors exists as well. On the contrary, the majority of the MWIR cameras require cooling, using either liquid nitrogen or a Stirling cycle cooler.[9] Cooling to approximately 196°C (77 K), offer excellent thermal resolution, but it might restrict the span of applications to controlled environments.
46. Minimum resolvable temperature difference (MRTD):It is a measure for assessing the performance of infrared cameras, and is inversely proportional to the modulation transfer function.
47. Modulation transfer function (MTF):It is used to approximate the position of best focus of an infrared imaging system. In an imaging system, best focus is typically achieved when the MTF is between 0.4 and 0.6; most often at 0.5 (50% cutoff frequency of the MTF).
48. Spatial Resolution-It is the measure of how closely lines can be resolved in an image. And it depends on properties of system creating the image, not just the pixel resolution in pixel /inch.IFOV, or Instantaneous Field of View (otherwise known as Spatial Resolution): It is the smallest detail within the FOV that can be detected or seen at a set distance.
49. Caliber:When the barrel diameter is given in inches, the abbreviation "cal" is used in place of "inches." For example, a small bore rifle with a diameter of 0.22 inch is a .22 cal; however, the decimal point is generally dropped when spoken, making it "twenty-two caliber" or a "two-two caliber". Calibers of firearms can be referred to in millimeters, as in a "caliber of eighty-eight millimeters" (88 mm) or "a hundred and five-millimeter caliber gun" (often abbreviated as "105 mm gun").
50. MOA (Minutes of angle):1 MOA subtends approximately one inch at 100 yards, a traditional distance on target ranges. Since most modern rifle scopes are adjustable in half (½), quarter (¼), or eighth (⅛) MOA increments, also known as clicks, this makes zeroing and adjustments much easier. For example, if the point of impact is 3" high and 1.5" left of the point of aim at 100 yards, the scope needs to be adjusted 3 MOA down, and 1.5 MOA right. Such adjustments are trivial when the scope's adjustment dials have an MOA scale printed on them, and even figuring the right number of clicks is relatively easy on scopes that click in fractions of MOA.
