Glossary of Terms
What does Automatic Brightness Control (ABC) mean
This allows the tube to protect itself from overexposure. It keeps the image within a certain brightness range with upper limit, meaning there is a limit to how bright a tube can get to prevent damage.
This is nothing else then PWM but for image intensifier tubes. Offering the tube better protection and preventing resolution loss in high light condition.
Almost every tube has them, bigger or smaller. These are dust-particles trapped in the tube during the manufacturing process and are almost impossible to avoid.
This is a defective MCP, meaning electrons are being released even if they shouldn't. This is a common phenomenon in well used older tubes. Their visibility can vary depending on the light exposure conditions.
Using a single image intensifier tube with both eyes.
Viewing a scene through two image intensifiers, i.e. one channel per eye.
Loss in visibility due to a bright light source. Common in Gen 0 and Gen 1.
A 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-shape lines. This is due to the structural bundles of with either the MCP or the fiber optic.
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.
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. Optical Distortion: Optical distortion occurs when the design of the optics causes straight lines at the edge of the field of view to curve inward or outward. This curving of straight lines at the edge will cause a square grid pattern to start to look like a pincushion or barrel. This distortion is the same for all systems with the same model number. Good optical design normally makes this distortion so low that the typical user will not see the curving of the lines.
Fiber Optics Distortions: Two types of fiber optics distortions are most significant to night vision devices: S-distortion and shear distortion:
S-Distortion: Results from the twisting operation in manufacturing fiber-optic inverters. Usually S- distortion is very small and is difficult to detect with the unaided eye.
Shear Distortion: Can occur in any image tube that uses fiber-optic bundles for the phosphor screen. It appears as a cleavage or dislocation in a straight line viewed in the image area, as though the line were sheared.
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.
The distance a person’s eyes must be from the last element of an eyepiece to achieve the optimal image area.
The angle of the visible area you see through your night vision device.
Figure of Merit (FOM)
Image Intensification tube specification designation, calculated on line pair per mm x signal to noise. (FOM=lp/mm * SNR)
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 "noisier" and the signal-to- noise ration many go down. Military Gen 3 image tubes operate at gains of between 20,000 and 45,000.
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).
An image intensifier protection feature builds in to the housing, incorporating a sensor, microprocessor and circuit breaker. This feature will turn the system off during periods of extreme bright light conditions.
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 and can cause headache and eyestrain.
The distance between the users pupils (eyeball centers). The 95th percentile of US military personnel falls within the 55 to 72mm range of IPD.
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. Image intensifiers operate in the near infrared spectrum and thermal devices operate in the far infrared spectrum.
Lp/mm (Line Pairs per Millimeter)
Units used to measure image intensifier resolution. 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, (Gen 2+ at 54-59 lp/mm typically), while a Generation 1+ tube may have measure at 40 lp/mm.
MCP (Microchannel Plate)
A metal-coated glass disk that multiplies the electrons produced by the photocathode. An MCP is found only in Gen 2 or Gen 3 systems. MCPs eliminate the distortion characteristic of Gen 0 and Gen 1 systems. The number of holes (channels) in an MCP is a major factor in determining resolution. Modern MCPs have about 10 million holes or channels compared to the previous standard of 3.14 million.
The input surface of an image intensifier tube that absorbs light energy (photons) and in turn releases electrical energy (electrons) in the form of an image. The type of material used is a distinguishing characteristic of the different generations.
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 (mA/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 photo response is in the 1800 mA/lm (2000 mA/lm for the latest Omni VI Pinnacle tubes), the actual number is more like 900 mA/lm.
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).
Reticle (Reticle Pattern)
An adjustable aiming point or pattern (i.e. crosshair) located within an optical weapon sight.
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.
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.
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. P-45 phosphor is used in the systems offered in this catalogue.
Stereoscopic Night Vision
When two views or photographs are taken through one device. One view/photograph represents the left eye, and the other the right eye.
When the two photographs are viewed in a stereoscopic apparatus, they combine to create a single image with depth and relief. Sometimes this gives two perspectives. However, it is usually not an issue because the object of focus is far enough away for the perspectives to blend into one.
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.