How To Buy Night Vision Device
- Night Vision Type
- Night Vision Generation and Performance
- Digital Night Vision
- Night Vision Magnification
- IR Illuminators
NIGHT VISION TYPE
Monocular
A monocular is an NV product that has one eyepiece and one objective. It usually refers to a unit that is held in the hands and is typically between 2x and 5x. An NV monocular has many advantages. It is the smallest NV unit, as well as the least expensive and it offers as much performance as a binocular or goggle. The only disadvantage of a night vision monocular is that it allows you to use only one eye when you observe. Over long observing sessions, this can create eye strain and fatigue, but, fortunately, most NV observing is intermittent, not continuous.
Binocular
An NV binocular is much the same as a daylight binocular in that it offers two eyepieces and two front lenses with the addition, of course, of an NV intensifier tube. An NV binocular still only uses one intensifier tube system, so it won't offer greater performance or range than a monocular, but it will provide more comfortable viewing since you are you using both eyes. However, an NV binocular will also be heavier and more expensive than an NV monocular.
Goggle
An NV goggle is any unit that comes with a headset. It comes in three versions:
- Monocular goggle - As the name suggests, this goggle uses a monocular mounted to a headset. This is the lightest and least expensive type of night vision goggle (night vision system), but since you are using only one eye and one optical system, it will not be as comfortable to use as a system with two eyepieces, not will it provide any depth perception.
- Bi-ocular goggle - The bi-ocular goggle feature two eyepieces, but only one front lens. This improves viewing comfort over a monocular goggle, but because there is only one front lens, there is no improvement in depth perception over a monocular.
- Binocular goggle - The binocular goggle uses two eyepieces and two front lenses. This not only provides better viewing comfort than a monocular, it also provides depth perception since it is using two different optical systems. This is an important feature if you are using a goggle while in motion, say walking or even driving off road.
NIGHT VISION GENERATION AND PERFORMANCE
The generation of an night vision device product will determine many things, principally performance and price. There are 4 generations of night vision in use, though new digital technology now makes digital NV units another option to consider.
Gen 1 Night Vision
This is the least expensive and oldest technology in night vision. All gen 1 intensifier tubes are made in the same factory in the Ukraine, so all Generation 1 Night Vision Devices will have roughly similar performance. (Gen 1+ indicates a current production tube, not a better grade of tube). Only features other than the intensifier tube that affect Gen 1 performance are objective size (large objectives supply more light), magnification (more is NOT better- this is a low resolution product) and the IR illuminator (need by all gen 1 products under tough conditions). If you are using an NV in a marine environment, be sure to use a waterproof model.
Gen units are easily identified. Gen units require 15-30 seconds to power up or power down and will always have some pronounced optical distortion (fish-eye distortion) at the edge of the field.
Gen 1 units can be used to about 75-100 yards to detect man sized objects under average conditions and perhaps a bit more under ideal conditions, say full moonlight. Detection range is defined as the range in which a target will present a recognizable silhouette. Recognition range is defined as the range in which a target begins to show recognizable detail. For most Gen 1 units, this will typically be 50-75 yards or less for a man sized object. It is important to understand that smaller targets will reduce both detection and recognition range.
Gen 2 Night Vision
The biggest gain in performance occurs between Gen 1 and Gen 2. With a gen 2 tube, you get much reduced distortion at the edge of the field, a screen with better contrast and resolution, better light amplification (less reliance on an IR for supplemental light) and improved tube life. This all translates into greater range, for both detection and recognition, typically another 50 to 75 yards on both, depending on the grade and type of tube.
Gen 2 also introduces options for grade and type of intensifier tube, though the designation of Gen 2+ indicates a current production tube, not a higher grade of tube. To check performance on a 2nd Generation Night Vision Device, you need to check for both resolution (lp or lpm) and type of tube. Special XD Gen 2 tubes, HDT Gen 2 tubes and SHD3 Gen 2 tubes approach Gen 3 Night Vision Device in performance, but also in price. They truly do bridge the gap between Gen 2 and Gen 3.
The most common measure of tube performance, and one that should always be checked on Gen 2 tubes and higher tubes, is resolution, stated in line pairs per millimeter (lpm) or sometimes just abbreviated as lp. As resolution goes up, so does price.
Gen 3 Night Vision
This is the highest generation of night vision technology commonly available and the generation currently employed by most military units and other serious users. Generation 3 Night Vision Units, under ideal conditions, are able to detect human sized objects at ranges of two hundred yards or more. As with Gen 2 units, there are many grades and options offered. Gen 3 tubes also offer vastly improved tube life and rarely, if ever, need to be replaced. All Gen 3 units are variations on the original AN PVS-14 (monocular) and AN PVS-7 (bi-ocular goggle) used by the military.
The most common measure of tube performance, and one that should first be checked on a gen 3 units is resolution, stated in line pairs per millimeter (lpm) or sometimes just abbreviated as lp. Other measures used for grading Gen 3 intensifier tubes include signal to noise ratio and screen quality (evenness of brightness and lack of dark spots), though these specifications are seldom listed or stated by manufacturer.
A grading system based on letters is sometimes used as follows for Gen 3. Intensifier tubes designated as Mil-spec must meet minimum military standards for all tube measurements and specifications. Since the origins of NV are military in nature, this is as good as it gets in NV performance. This is also the most expensive and difficult to obtain grade of NV , especially during wartime. Next are tubes that do not meet mil-spec standards. These are typically referred to as commercial grades. A commercial Grade A tube will typically fall short of mil-spec in just one measurement, often with only a minor dark spot on the screen. It may otherwise offer as much resolution as a mil-spec tube. Check the specs. A Grade B commercial tube typically falls short of mil-spec in more than one measurement, though the lower price may make it a good option.
Gen 4 Night Vision
This generation of night vision optics is not commonly seen or produced and was developed as an option for the military, who chose not to adopt it. Generation 4 Night Vision Devices is not as affected by bright light as other generations of NV , but tube life is reduced compared to a Gen 3. Performance is otherwise on a par with the best Gen 3.
Digital Night Vision
The same technology used in digital cameras, using CCD chips and CMOS chips to collect light, is also finding its way into night vision equipment and, like any other digital product (digital night vision) category, advances are being made rapidly. The first of these "digital viewers" to appear were on a par with a typical Gen 1 unit, but newer versions of digital night vision monoculars are now approaching performance that of a Gen 2 unit.
The advantages of going digital are significant. A digital monocular with Gen 2 like performance will be less than half the price of a standard Gen 2 night vision monocular. Digital night vision units are also easier to use with cameras, since you can attach any camera or camcorder equipped with a video input to the digital night vision unit with a simple RCA video cord. This circumvents the need to find an adapter, which is a problem with most conventional NV units. Lastly, digital units are not damaged by exposure to bright light, as are most conventional night vision products.
MAGNIFICATION
Night vision technology is about seeing in the dark; it is not about seeing great distances. Simply put, no night vision product (night vision goggles, night vision binoculars, night vision scope, night vision rifle scope, night vision monocular, night vision googles, night vision monoculars) will have the optical resolution of conventional daytime instruments such as binoculars, riflescopes, monoculars and so on. Because of this limit on resolution (screen sharpness), magnification in night vision products is limited, with 5x or 6x being about maximum. The problem, in a nutshell, is that as magnification goes up, image quality in night vision goes down. Excess magnification in this technology degrades the image to the point of being useless. Best image quality in conventional night vision technology is usually obtained at 1x (normal vision, no magnification) to about 3x. Field of view, image steadiness and overall ease of use is also better at these lower magnifications.
IR ILLUMINATORS
IR illuminators were originally designed to offer supplemental light for close up work, such as reading maps and, as such, are limited in their power, despite advertising claims to the contrary. For example a 450 milliwat model offers about half the wattage of a standard penlight flashlight. In a nutshell, an IR will not offer much help beyond 50-75 yards or so, but it will add considerable detail at closer ranges. An IR illuminator is a must for any night vision unit being used in total darkness, for instance, in the confines of a darkened building, where there is no ambient light. All Generation 1 units will need the assistance of an IR for most applications.
Jne K.
