Night Vision Devices (or Image Intensifiers as they are also known) are a military invention, designed to allow you to literally see in the dark.
Near the end of the second world war, both sides developed very crude active Infra-Red devices. These units were very bulky and not very effective, and had a major drawback - both sides could see the other if they turned off their IR source. It was not until the Vietnam war that passive Image Intensifying devices were developed and used in combat.
Modern Night Vision Monoculars, Bi-Oculars, Binoculars and Goggles are devices that amplify available ambient light levels in order to transform a very dark night time scene into a bright picture enabling the user to recognise features and objects that would otherwise remain masked by darkness.
Light enters the device via the objective lens, where it is focussed on a phosphor screen, which the user views through the eyepiece lens (the screen translates the image into a green picture - the human eye is particularly sensitive to differences in shades of green).
 Front Lens;  Photocathode;  Microchannel Plate;  High Voltage Power Supply;  Phosphor Screen;  Eyepiece;  Image Intensifier
The objective lens (1) of a night vision device collects light that can’t be seen with the naked eye and focuses it on the image intensifier (7). Inside the image intensifier a photocathode (2) absorbs this light energy and converts it to electrons. These electrons are then drawn toward a phosphor screen (5). In 2nd and 3rd generation intensifiers the electrons first pass through a microchannel plate (3) that further multiplies them thousands of times. When this highly intensified electron image strikes the phosphor screen (5), it causes the screen to emit visible light. Since the phosphor screen emits this light in exactly the same pattern and contrast as collected by the objective lens, the bright nighttime image seen through the eyepiece corresponds precisely to the observed scene.
Irrespective of the type or cost of a Night Vision system, this technology will only function passively if there is some ambient light available to be intensified.
In other words, your scope cannot function under conditions of Complete darkness - e.g in caves, completely blacked out buildings, in dense forest on a cloudy night etc. In these situations, it may be necessary to actively supply some light to assist the scope. This is done, not with ordinary white light, but with invisible (to the naked eye) Infra Red light, which illuminates the scene sufficiently for the scope to generate a clear bright image. Virtually all civilian NVDs have a built in IR illuminator for use in conditions of zero light, or to enhance the picture clarity to a level acceptable for other applications e.g Night Vision Video/Stills photography.
TYPES OF IMAGE INTENSIFIER
Image Intensifiers are currently classed into 3 main Generations (types), and each Generation has its own particular characteristics (and price tag !).
First Generation equipment was the first true passive image intensification technology, and is now the type most commonly used in civilian applications. GEN 1 scopes will function very well under conditions of 1/2 moonlight and brighter, and generally give a clear, high resolution picture. The GEN 1 photocathode is most responsive and sensitive to the visible light spectrum, but can also be enhanced with IR light in extremely low light levels. This type can be easily damaged beyond use if subjected to bright light/daylight, so care must be taken not to switch them on in light (without the supplied lens cover in place, and even then for short periods only). GEN 1 is also characterised by the fact that the tube stays warm for up to a few minutes after the scope is powered off, so the scope will still provide an image and appear to remain on until it cools down. Typical system gain for GEN 1 is 500 - 2000 times. GEN 1 is suitable for most civilian applications, where reasonable overall performance is achieved at a relatively low cost.
By using a more sensitive photocathode, better electronics and the inclusion of a micro-channel plate, GEN 2 devices give amazing performance. GEN 2 is more sensitive then GEN 1 in the near invisible IR light spectrum, and consequently will allow you to see further, with more clarity and under darker conditions then earlier technology. This Generation also exhibits very little image distortion and usually has both Automatic Brightness Control and Bright Source Protection Circuits, which give consistent picture brightness and protection against over exposure to bright light. Like GEN 1, GEN 2 can be assisted by IR light, but being more sensitive to this area of the light spectrum, the same amount of IR will be much more effective in range and magnitude when used with GEN 2 devices. Typical system gain for GEN 2 is 10 - 20,000 times.
GEN 2 is suitable for demanding civilian, scientific and military applications, where high performance is required in very low light levels.
This technology is current military issue. US Gen 3 is not available legally in Europe for sale to civilians (The US State Department will only authorise export licences to Government end users outside the USA). It is for this reason that we do not sell US Gen 3, but do stock high performance non-US Gen 3 sourced elsewhere.
GEN 3 is very similiar to GEN 2 in its internal layout, but uses a different chemical in the photocathode for even higher photosensitivity, spectral response (in the IR spectrum) and longer tube life. GEN 3 can be used passively in the darkest of conditions, giving a typical system gain of 40 - 65,000 times. GEN 3 devices are also characterised by a staggering price tag 1
The European equivalent technology of US Gen 3 (but which is actually Gen 2+ but developed to a very high performance level )is often referred to by its trade-marked brand-names ("SuperGen", "XD-4, XR-5" etc). By using highly sophisticated tube technology, the European manufacturers have developed film-less tubes (tubes that will give long life without a protective ion-barrier film) that allow all the electrons generated by the photo-cathode to enter the MCP. This results in the tubes being super efficient, and being able to compete with Gen 3 technology regarding performance in low-light levels. They out-perform Gen 3 in urban areas, where the European tubes give virtually no "halo" where bright light sources are present, while US tubes do.
Though it contains an IR sensitive camera and screen (rather than an intensifier tube) so-called "digital night vision" is still useful for viewing and hunting devices provided the use of plenty of infra red illumination is not an issue. There are many advantages to this technology - it can be used in daylight with no risk of damage, most units have a video out facility so recording what you are viewing is very straight-forward, cost is generally a lot lower than real night vision devices etc.
FACTORS TO BE CONSIDERED BEFORE BUYING NVE
There is a vast array of NVE available for civilian use on the market to-day, with each manufacturer making his own claims as to why you should buy his product. We can demonstrate products and advise you backed up by our experience, but in the end, the decision is yours. Before making that decision, please consider the following factors carefully.
PRICE: The technology involved in NVE is, by its nature, costly, so price is an important factor. Will the use that you get from your NVD justify the expense? Our prices range from just over £200 to over £5,600. While top of the range scopes are technically awesome and offer great value for money in terms of the results that they produce, your needs will more then likely be satisfied by a high quality monocular or binocular for under £1000. If you require a device for a professional purpose, please contact us for advice.
SIZE, WEIGHT AND EASE OF OPERATION: If a device is not comfortable to hold and easy to operate, it will become a burden rather then an aid, and will be of little benefit to you. This factor has a lot to do with the conditions that you want the device to work under - if you intend to be very mobile while using your NVD, a small light model may suit ; however, if you intend to view from a static position, you may be able to manage with a larger model. Whatever the type or model, the switches and focus control on the device should be positioned where they can be adjusted easily by touch - remember that you will be using the device in the dark. If you are going to observe for extended periods of time, a Bi-ocular or Binocular model may be appropriate, which because it allows you to view with both eyes, will make observation less tiring, affording you more operational comfort.
BATTERIES: All NVDs for civilian use are powered by readily available batteries, usually either alkaline or lithium. The cost of replacing batteries is something that you should consider - alkaline batteries give shorter life but are cheap to replace, and can be bought in any newsagents. Lithium batteries give longer life but are more expensive, and are usually found on sale in chemist/camera shops.
RELIABILITY: Provided that they are not abused e.g exposed to bright light, violent treatment or excessive moisture, modern NVDs are extremely reliable and are rated to give a long and trouble free life. In addition, all of our devices (unless specified) are covered by a minimum one year warranty (devices manufactured by AMT Corp. carry a two year warranty) subject to correct and responsible use. By following the guidelines and instructions included with each device, your NVD will give you many years of valuable service. We do NOT deal in, or recommend that you buy, secondhand NVE. Image Intensifier tubes become de-sensitised and eventually fail, after repeated exposure to bright light ; with secondhand equipment you have no indication as to the remaining life left in the tube (due to prior use/abuse) until the tube fails. We recommend that you only buy new, guaranteed equipment, and even then you must always keep the objective lens cover on in bright conditions and avoid testing the devices protection circuits unnecessarily.
WHAT TO LOOK FOR WHEN SELECTING AN NVD
The best way to choose your night vision equipment is to evaluate it under the conditions that you require it to work for you. To this end, we are happy to demonstrate devices to you, in order to help you make an educated choice. However, you should consider the following interdependant performance factors before deciding on a particular type or model.
MAGNIFICATION: Just because the objective lens gives a high magnification e.g 5 X or 8 X, it does not always mean that it will give you a better or more detailed picture. Increased magnification will usually reduce the amount of light that the lens can capture, so that more tube gain will be necessary to give an acceptably bright picture under very dark conditions. Your units effective range depends on a combination of available light, magnification, gain and resolution.
GAIN: This is the number of times that the device amplifies the ambient light level. It is expressed in two ways - either as Tube Gain or System Gain. Tube gain refers to the amount of gain measured from the intensifier tube only, and is not an accurate bench mark of the performance of the device as a whole. System Gain refers to the overall gain of the device, considering the lens, II tube, filters and phosphor screen ; this is a much more accurate measurement because it measures all the components working together (gain values that we gave earlier for the different generations were typical system gains) and is usually a much smaller figure then the tube gain. Surprisingly, more gain does not necessarily mean a clearer or better picture, but merely a brighter picture. Tubes that work a very high gain value may as a result have a shortened life span because they are under much higher tension.
RESOLUTION: This is the ability of the NVD to allow the user to distinguish the shape and line of objects situated in close proximity to each other, and it is this factor which enables the user to make out details on objects rather then just there outlines. Resolution is normally expressed as line pairs per millimetre (lp/mm).
COMMONLY USED TERMS EXPLAINED
ANGLE (FIELD) OF VIEW: The measure of the width of the scene as viewed through the NVD - usually higher magnification lenses will give a smaller field of view.
AUTOMATIC BRIGHTNESS CONTROL: This is a protection and anti-glare circuit that gives consistent picture brightness on the viewing screen irrespective of the level of light entering the device (as light levels on the target area rise, the scope automatically dims, and vice versa).
BINOCULAR: An NVD that has 2 seperate objective lens, 2 seperate intensifier tubes and 2 seperate eyepiece lens. Binoculars are great for long term observation, (because they do not tire the eye to the same degree as monoculars) and also give true depth of field, enabling the user to judge distances more accurately.
BI-OCULAR: An NVD with a single objective lens, single intensifier tube but with 2 seperate eyepiece lens. Like Binoculars, they are good for long term observation and are more comfortable to use over long periods then a monocular.
BLACKSPOTS: Artefacts which appear on the viewed scene. These are quite normal and are inherent in the manufacturing process (they are graded into permissible sizes and numbers per tube) Spots can also appear on the viewed scene because of burn-in i.e where the NVD has been exposed to very bright sources of light for long periods (the area of the photocathode exposed no longer produces electrons and appears as a dark spot on the image.
BLOOMING: This is an attribute mostly associated with GEN 1 and earlier GEN 2 models. Bright light in the field of view produces a fog-like glare on the image, which remains for a few seconds as an after-image, and is most noticeable when the user has panned from a bright to a dark scene.
BRIGHT SOURCE PROTECTION: A protection circuit that cuts the power to the NVD if brightness levels are too high for the device to take, and which would result in the tube being damaged. The BSP circuit normally resets after a few minutes, if light levels drop.
DISTORTION: This is where the image as shown in the device deviates from the true life image ; There are 3 main types of distortion - Geometric, Shear and "S". The latter two are barely noticeable to the naked eye, but geometric distortion can be quite visible (especially in GEN 1 devices) and appears as a slight curving of the image in the periphery zone.
FIXED PATTERN NOISE: When GEN 2 and GEN 3 devices are used in very high light levels, a pattern of hexagonal shapes (similiar to a honeycomb) becomes visible on the image. This is actually the shape of the micro-channel plate being pronounced by the incoming light, the small hexagonal shapes being the rods of the MCP. This pattern disappears when the scope is used under the dark conditions.
GAIN: The level to which the image intensifier will amplify (intensify) the existing ambient light. Tube gain gives a very impressive figure but is actually pretty meaningless to the layman (a 5000 horse power engine may sound very powerful, but not if it is pulling an oil tanker !). System Gain is a far more useful and accurate specification, because it takes into account the entire device including loss of light from objective lens, electronic filters, phosphor screen and eyepiece lens.
GALLIUM ARSENIDE: Or GaAs for short. Gallium Arsenide is the highly photo-sensitive chemical used in GEN 3 sytem photocathodes, which accounts for their high performance in low light levels and their very long tube life span.
INFRA-RED: This is light that is invisible to the naked eye because it is outside our eyes light spectrum level (usually 750+ nanometers) but is visible through Night Vision Equipment (all generations, but more so through GEN 2 and most of all through GEN 3).
LEN SPEED: The ability of a lens to gather light. Lower f numbers are faster i.e they gather light more effectively.
MICRO CHANNEL PLATE: This is the metal covered glass plate which makes GEN 2 and GEN 3 systems so effective. It contains millions of holes (called channels or rods) through which electrons from the photocathode pass. As they do so, they bounce off the walls of the channels and propel many more electrons down through the channel, so that for every single electron that enters from the photocathode, many thousands exit to strike the phosphor screen and create the image that the user sees. Naturally, the more channels that the MCP has, the higher the resolution of the resultant image.
MONOCULAR: An NVD with a single objective and a single eyepiece lens. Usually suitable for most applications, but especially where a smaller unit is required for convenience reasons. Monoculars are handy where the user has to move around during use - your eyes quickly revert back to natural night vision where only one eye has been exposed to bright light (from the NVD) - enabling the user to rely only on his eyesight for orientation while moving. (Binoculars - because the user views with both eyes - tend to diminish your eyes natural night vision, making your eyesight less effective in dark conditions for up to 20 minutes after use, as if the user had just stepped from a bright room into the darkness).
NOISE: Also called scintillations. This appears in the eyepiece of NVDs as a sparkling effect on the image, and is more pronounced in GEN 2 and GEN 3 systems, when used in extremely low light levels (caused by stray electrons from the MCP striking the phosphor screen).
OPTICS: Any lens or ancilliaries used as part fo the NVD. Only the highest quality optics make the grade when it comes to NVE, and usually those with the best light gathering ability.
PHOSPHOR SCREEN: A screen that the user views through the eyepiece lens. The screen gives off a green glow when struck by electrons from the II tube, and it is this process that creates the image that the user sees. (As previously stated, green phosphor is used because the human eye is most sensitive to subtle changes in the colour green).
PHOTOCATHODE: This is situated at the front of the image intensifier. The objective lens focusses the image onto the photocathode, which when struck by light photons, sends off corresponding electrons into the intensifier tube. The more sensitive the photocathode to the invisible IR spectrum the better.
PHOTOSENSITIVITY: The sensitivity (or efficiency) of the photocathode expressed as a value (the higher the value, the more efficient the performance in low light).
RESOLUTION: The ability of an NVD to give a detailed picture, that will enable the user to distinguish between objects situated close together and see their physical characteristics. Resolution is a very important contributing factor to the successful performance of any NVD.
SPECTRAL RESPONSE: This is the term given to the sensitivity of the photocathode to different wavelengths of light - this is also a very important factor in the NVDs performance capability. The further down into the invisible Infra Red spectrum that the device can operate, the better its performance will be at low light levels - at night there is always more light available in the IR spectrum then there is in the visible light region (otherwise it would not be dark !!). GEN 1 spectral response is in the near visible light region, while GEN 2 goes further down into the invisible IR spectrum, and GEN 3 further again.
WEAPONSIGHT: An NVD that can be mounted onto a firearm enabling the user to engage targets at night time, more or less as you would during daylight.
Q. How far will I be able to see with my NVD ?
A. This is the question most often asked, and the one that is most difficult to answer. Not only is the performance of any particular scope limited by the amount of ambient light (moon/starlight, cloudglow, artificial light etc), but it is also limited by prevailing weather conditions (fog, mist, heavy rain) which will also limit its performance. Under ideal conditions, the range of the device is dictated by the interdependant factors of magnification, resolution and gain, and naturally these factors are different for nearly every device. The best effective range with most intensifiers is achieved with a high speed lens that has minimal magnification ( less then 5 X), a high resolution factor and enough gain to make the image bright without creating "noise" (often referred to as scintillations) on the image. Range (to the layman) is best expressed as Detection Range and Recognition range - where the device is tested under specific levels of light e.g starlight, 1/4 moon, 1/2 moon, full moon. Detection Range is the range at which you can make out the human form against a contrasting background, see vague outlines and detect movement. Recognition range is the range at which you can easily recognise details on a person or object (not just outlines) and can clearly make out shapes and features.
Where possible, we try to quote these performance distances in our specifications (using conditions of 1/2 moon +) and invariably these distances will be greater with GEN 2 devices.
Q. If I am looking through my scope, and someone turns on a bright light within my field of view, Will I be blinded ?
A. No, but this is something that nearly every film maker deems necessary to include in his script, if a film involves Night Vision Devices ! The truth is that if your scope is of a very simple design, the tube will cease to function in a matter of a second or so, before any damage can be done to your eyes. If your scope is of a more modern design, its protection circuits will cut all power to the tube ( nearly instantly) if light levels get too high. These self-preservation systems are Automatic Brightness Control (ABC) and Bright Source Protection (BSP). The former adjusts screen light levels to a constant level, and if the amount of light entering the scope is too much for the ABC to control, the latter cuts the tube power for a period of 2 minutes, before powering up again. These protection circuits should be seen as a safety feature only, and should NOT be tested unnecessarily.
Q. What is " Blooming " ?
A. When an NVD is panned across bright light sources, the light may leave a hazy, streaky afterglow which will degrade the image on the screen for up to 30 seconds after the user has panned on ; this is known as blooming. Modern GEN 2 and GEN 3 scopes have nearly eliminated this characteristic, but the less advanced GEN 1 scope is still adversely affected by it.
Q. Why are there small black spots on the picture ?
A. Black spots (which appear in scope picture resembling dust) are small cosmetic imperfections in the tube which are a perfectly normal attribute of NVE and inherent in the manufacturing process of the tube. A permissible number of these spots is shown later on, and where the number and size of these spots exceeds these guidelines, the tube is considered to be sub-standard. Spots may also appear in the tube if a scope has been exposed to a bright light source for long periods of time (the areas of the tube that are most exposed to the light become deficient in electrons, and subsequently become completely de-sensitised, and appear as black spots).
Q. Will my Night Vision Device pick up body heat ?
A. No, absolutely not. NVDs amplify available ambient light, whereas Thermal Imagers ( a completely different technology) pick up differences in temperature. This technology is still out of the reach of the average person, being immensely expensive.
Q. Can I mount my NVD to a camera or camcorder ?
A. It is possible to mount some of our units in this way for photographic purposes. Our catalogue will let you know which units are adaptable. Incidentally, GEN 2 units will generally give the best results for this purpose.
Q. How long will my NVD last ?
A. Most image imtensifier tubes (depending on generation ) will last between 2,000 and 4,000 hours, depending on the conditions that they are used under (continuous exposure to bright light will shorten the tube life). Keep in mind that if you use your unit for 100 hours a year, you are using it a lot, and even in this case the expected life from even a GEN 1 unit could be 20 years !
Q. Why are Night Vision devices so expensive ?
A. The technology and machinery involved in the manufacture of NVE is awesome, and therefore does not come cheaply. It can take over 6 weeks to make a single II tube, involving over several hundred manufacturing steps. The failure rate is quite high, which in turn pushes up the unit cost.