Glossary

Automatic Brightness Control (ABC)

An electronic feature which automatically reduces voltages to the micro channel plate to keep the image intensifier’s brightness within optimal limits, and protects the tube. The effect of this can be seen when rapidly changing from low-light to highlight conditions; the image gets brighter and then, after a momentary delay, suddenly dims to a constant level.

Biocular

Viewing a single image source with both eyes (example: watching a television set).

Binocular

Viewing a scene through two channels; i.e. one channel per eye.

Black Spots

Cosmetic 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.

Bore Sighting

The alignment of a weapon-aiming device to the bore of the weapon.

Bright Source Protection (BSP)

An electronic feedback circuit that automatically shuts down the image when a bright flash enters the scene.

Daylight Lens Cover

Usually made of soft plastic or rubber with a pinhole, which allows a small amount of light to enter the objective lens of a night vision device. This should be used for training purposes only, and is not recommended for an extended period of time.

Daylight Training Filter

A glass filter assembly designed to fit over the objective lens of a night vision device. The filter reduces light input to a safe (nighttime) level, allowing safe extended daytime use of the night vision device.

Diopter

The unit of measure used to define eye correction or the refractive power of a lens. Adjustments to an optical eyepiece accommodate for differences in individual eyesight. Most systems provide a +2 to -6 diopter range.

Eye Relief

The focus-range distance between the user’s eye and the eyepiece lens of an optical device at which the viewed scene can clearly be seen.

Field of View

The diameter of the imaged area when viewed through an optic.

Focus Range

The range within which an optical device can be adjusted or focused on a target.

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. 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 (Ga As):

The semiconductor material used in manufacturing the GEN III photo cathode.

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 technology or manufacturing process that improved since the previous generation.

GEN I

Vietnam Era technology. GEN I has the most distortion and the least tube life. GEN I image tubes are most commonly found in imported night vision devices.

GEN II

1960s development of micro channel plate (MCP) amplifier component provided the needed breakthrough for high gain and small size.

GEN II+

1970s development increased image tube bias voltage to improve gain. Additionally, a glass faceplate was added to improve resolution.

GEN III

1980s development provided substantially improved gain and a bandwidth which reached farther into the near IR region. Improvements in the micro channel plate. (MCP) and a gallium-arsenide photo cathode greatly enhanced tube life and performance.

GEN III+

Generally referred to as GEN III Enhanced, 1990’s improvements in the photo cathode and MCP resulted in increased gain and resolution. Not a generally accepted term, but used herein for brevity.

GEN IV

Commonly referred to as (but not official): 4th Generation or Gated Filmless technology represents the biggest technological breakthrough in image intensification of the past 10 years by removing the ion barrier film and gating the system. Gen 4 demonstrates substantial increases in target detection range and resolution, particularly at extremely low light levels.

High Light Shutoff

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.

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 centers). The 95th percentile of US military personnel falls within the 55 to 72mm range.

IR Illuminator

Many night vision devices incorporate an infrared (IR) diode which emits invisible light. IR light cannot be seen by the unaided eye; therefore, a night vision device is necessary to see this light.

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.

Image Intensifier Tube

A high-vacuum device, which collects photons and amplifies these as electrons. This amplification of photons allows the viewer to see more light than without a night vision device.

LIF

Laser Interference Filter Line Pairs per Millimeter (lp/mm) – Units used to measure image intensifier resolution.

Low Voltage Indicator

A warning device in a night vision system that signals low battery power.

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.

Micro Channel Plate (MCP)

A metal-coated glass disk which multiplies the electrons produced by the photo cathode. Found only in GEN II and GEN III systems, the MCP can have between 2 and 6 million holes (or channels) in it.

MIL-SPEC

Term for Military Specification. It is the minimum acceptable requirements for products procured by the Department of Defense. Use of the term MIL SPEC indicates that the product meets applicable military specifications.

Monocular

A single-channel optical device.

Photo Sensitivity (Photo Response)

Also called photo cathode sensitivity. The ability of the photo cathode material to produce an electrical response when subjected to light waves (photons). The higher the value, the better the ability to produce a visible image under darker conditions.

Resolution

The ability of an image intensifier or night vision system to distinguish between objects close together. 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.

Scintillation

Also known as electronic noise. A faint, random, sparkling effect throughout the image area. Scintillation is a normal characteristic of micro channel plate image intensifiers and is more pronounced under low-light-level conditions.

Screen

The image tube output, which 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-20 phosphor is used in most systems.

System Gain

Equal to tube gain minus losses induced by system components such as lenses, beam splitters, and filters.