Night time has long been the friend and province of the predator. Because of the human beings’ very limited night vision capabilities, his nocturnal activities have always been strictly limited. His abilities to observe the world around him during the hours of darkness, were similarly restricted.

Since the Second World War, the steady increase in the capabilities of equipment designed to enhance the night vision capabilities of the human being, has resulted in a range of binoculars and other equipment that, for a price, can banish the darkness.

Whilst not providing the same clarity of image as that delivered by their daylight counterpart, night vision binoculars have developed to such a high degree, that most things that were hidden by the darkness can now be seen at an adequate level of clarity to permit detailed observation, depending on the magnification of the device.

Indeed, the very latest technology, enable law-enforcement and military operations in visual conditions not far removed from broad-daylight. Not generally available to the public currently, the price tag for this level of performance is prohibitive to say the least.

So how does this equipment work?

Some may wonder how exactly night vision binoculars are able to see in the dark. The reason is that the optical design of these binoculars is developed in such a way that the binoculars will locate existing light in an environment and then amplify it. This includes both light that is visible to the human eye and light that falls under the category of the infrared spectrum. When you look through the binoculars, you will see things through a green vista screen. This is because you are not looking directly through the lens of the binoculars. You will be looking at images in a phosphor screen.

Night vision binoculars are electro-optical devices. Available light from the moon and stars is gathered by the objective lens and strikes a highly charged optical cathode. This fires electrons across a vacuum tube, intensifying the image in the process, to strike a phosphor screen. This provides the ghostly green image which typifies most night vision images. The green color was chosen because the human eye can identify more shades of green than any of the other available phosphor colors. The optical eyepiece then magnifies the image, which the user then views. So when using night vision binoculars, you’re not actually looking through the device, your looking at a screen which displays the intensified image.

Whilst they are a solution to seeing in the dark they do have a couple of drawbacks.

The electronics are powered by batteries, which increases the weight of the device. If the batteries go flat, no more viewing, unless replacement batteries are to hand.

Despite the drawbacks, for night time hunting or fishing, or watching the nocturnal behavior of the wild-life in your neck of the woods, then night vision binoculars are the answer to your prayers.

Those that are fans of spy and action movies have surely seen night vision binoculars prominently featured in the proceedings. Some may assume that night vision binoculars are exotic items to be used solely but the military. Actually, this is not the case as these binoculars have been used by anyone for hunting, security work, and just for fun. Of course, to use these binoculars you will have to find a decent pair to purchase. To truly understand which binoculars fit your needs, it is helpful to understand a few basic facts about them.

Light Availability

It is also important to point out that since there are different levels of darkness, there will need to be different types of night vision binoculars designed to handle the low light scenarios. This is why when you purchase these binoculars, it is important to ascertain the generation levels on them. These generation levels are labeled 1 to 4. Generations 1 and 2 are for common use. That is, generation 1 and 2 can be used for common, low light scenarios. Generation 3 and 4 are significantly stronger and operate in extremely low light scenarios. As such, generation 3 and 4 binoculars are used mainly by professionals who would have need of them. In order to select the pair of binoculars that would suit you best, it would be helpful to ascertain what type of light scenario you wish to use them in.

Another important factor one should look at when purchasing these binoculars centers on realizing the range of the binoculars. Some binoculars have very limited range while others will be able to reach extended distances. Understanding the range that the binoculars can cover is very important in making the right selection for your purchase. After all, if the binoculars lack the needed range for their intended purpose, they will not deliver the value for their price.

Some may also be concerned with the cost of night vision binoculars. It is true that these items can come with high price tags. However, there are situations where you can purchase a lower cost version of these binoculars. Namely, you can purchase a single vision monocular as it comes with a much lower price tag. So, yes, there are options for those that are on a budget and there is no need to assume you have been priced out of the market for night vision devices.

NIGHT VISION TERMINOLOGY

From here until the end, we are referring specifically to Night Vision products

Automatic Brightness Control (ABC)
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.

Auto-Gated Power Supply
When the power supply is “auto-gated,” it means the system is turning itself on and off at a very rapid rate. This, combined with a thin film attached to the microchannel plate (an ion barrier) reduces blooming. While “blooming” can be noticeably less on systems with a thin film layer, systems with thicker film layers can be perfectly acceptable depending on the end user’s application. Deciding which night vision goggle is better should not be based solely on blooming.

Black Spots
These are common blemishes in the image intensifier of the NVD or can be dirt or debris between the lenses of the NVG. Black spots that are in the image intensifier do not affect the performance or reliability of a night vision device and are inherent in the manufacturing processes. Every night vision image intensifier tube is different. They are like diamonds. See image to the right. See also – How to Buy Night Vision Equipment

Bright Spots
These can be defects in the image area produced by the NVG. 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.

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.

Blooming
Loss of the entire night vision image, parts of it, or small parts of it, due to intensifer tube overloading by a bright light source. Also, known as a “halo” effect, when 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, become much brighter, “whiting out” objects within the field of view. Blooming is common in Generation 0 and 1 devices. The lights in the image to the right would be considered to be “blooming”.

Bright-Source Protection (BSP) – High-Light Cut-Off
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.

C-Mount
A standard still and video camera lens thread size for mounting to the body of a camera. Usually 1/2″ or 3/4″ in diameter.

COMSPEC (Commercial Specification)
A term used to describe image tube quality, testing and inspection done by the original equipment manufacturer (OEM).

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 wwill form hexagonal or square wave-shape lines.

Daylight Lens Cover
Usually made of soft plastic or rubber 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 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 (night-time) 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. Usually, adjustments to an optical eyepiece accomodate for differences in individual eyesight. Most ITT systems provide a +2 to -6 diopter range.

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.

Classical Optical Distortion:

Occurs when the design of the optics or image intensifier tube 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 Manufacturing 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 use fiber-optic bundles for the phospor 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 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.

Edge Glow

There is a defect in the image area of the NVG. Edge glowis a bright area ( sometimes sparkling) in the outer portion of the viewing area.

EmissionPoint
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.

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.

Field-of-View
The diameter of the imaged area when viewed through an optic

Figure of Merit (FOM)
Image Intensification tube specification designation, calculated on line pair per mm x signal to noise.

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 2 and Gen 3 systems if the light level is high enough.

Footlambert(fL)
A unit of brightness equal to one footcandle at a distance of one foot.

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” and the signal-to-noise ration many go down. 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.

Generations
Two technologies are referenced as night vision; image intensification and thermal imaging (see definitions). Because of cost and the fact that image intensifier scenes are easier to interpret than thermal (thermal images show targets as black or white – depending upon temperature – making it more difficult to recognize objects), the most widely used night vision aid in law enforcement is image intensification equipment.

Generation 0
The first night vision aids (also called Generation Zero or Gen 0) were sniper scopes that came into use during World War II and the Korean conflict. These were not true image intensifiers, but rather image converters, which required a source of invisible infrared (IR) light mounted on or near the device to illuminate the target area.

Generation 1
The “starlight scopes” developed during the early 1960’s for use in Vietnam were the first Generation (Gen 1) of image intensifier devices. In Gen 1 night vision units, three image intensifiers were connected in a series, making the units longer and heavier than future night vision units would be. Gen 1 equipment produced an image that was clear in the center of the field of view but suffered from large optical distortion around the periphery. Gen 1 equipment was also subject to “blooming”. Most low-cost imported night vision units use Gen 1 technology, though often under the guise of a higher “generation”.

Generation 2
The development of the microchannel plate, or MCP, in the late 1960s brought on the second generation (Gen 2) in night vision. The MCP accelerated and multiplied electrons which provided the gain previously supplied by coupling three image intensifiers together (Gen 1). The introduction of the MCP significantly reduced size and weight for image intensifier tubes, enabling 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. The Gen 2 tubes used the same tri-alkali photocathode as the Gen 1 devices. This generation was implemented to reflect the change in how the light was amplified (MCP versus three-stage coupling).

Highlight 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.

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.

Lumen
Denotes the photons perceptible by the human eye in one second.

Monocular
A singlechannel optical device.

Photocathode:
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.

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).

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 microchannel plate image intensifiers and is more pronounced under low-light-level conditions

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. P-20 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 ususally not an issue because the object of focus is far enough away for the perspectives to blend into one.

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.

Zeroing
A method of boresighting an aiming device to a weapon and adjusting to compensate for projectile characteristics at known distances.