Night Vision Buying Guide and Night Vision Facts
How Does Night Vision Work?
That’s a common question that we are asked. Need a quick night vision intro? Take a look at our night vision information section or read below for some quick tips.
Night Vision Buying Guide and Night Vision Facts
Night vision devices gather existing ambient light (starlight, moonlight or infra-red light) through the front objective lens. This light, which is made up of photons goes into a photocathode tube that changes the photons to electrons. The electrons are then amplified to a much greater number through an electrical and chemical process. The electrons are then hurled against a phosphorus screen that changes the amplified electrons back into visible light that you see through the eyepiece ( ocular lens ). The image will now be a clear green-hued amplified re-creation of the scene you were observing.
A Night Vision Device can be either a 1st, 2nd, or 3rd generation unit. What this stands for is what type of light intensifier tube is used for that particular device The light intensifier tube is the heart and soul of an NVD.
1st generation is currently the most popular type of night vision in the world. Utilizing the basic principles described earlier, a 1st generation will amplify the existing light several thousand times letting you clearly see in the dark. These units provide a bright and sharp image at a low cost, which is perfect, whether you are boating, observing wildlife, or providing security for your home. You may notice the following when you are looking through a 1st gen unit, a slight high-pitched whine when the unit is on. The image you see may be slightly blurry around the edges. This is known as Geometric Distortion. When you turn a 1st gen off it may glow green for some time. These are inherent characteristics of a 1st gen and are normal.
2nd generation is primarily used by law enforcement or for professional applications. This is because the cost of a 2nd gen unit is approximately $500.00 to $1000.00 more then a 1st generation unit. The main difference between a 1st and a 2nd generation unit is the addition of a micro-channel plate, commonly referred to as an MCP. The MCP works as an electron amplifier and is placed directly behind the photocathode. The MCP consists of millions of short parallel glass tubes. When the electrons pass through these short tubes, thousands more electrons are released. This extra process allows 2nd generation units to amplify the light many more times then 1st generation giving you a brighter and sharper image.
3rd generation is the latest in night vision technology. By adding a sensitive chemical, gallium arsenide to the photocatnode a brighter and sharper image was achieved. However, it is vastly more expensive then 1st or 2nd generation. Typically a 3rd generation unit will cost in excess of $3000.00.
How Far Can You See With A Night Vision Device?
There are many different variables that can affect the distance that you can see with a Night Vision device. First, what are you trying to see? Are you looking for another boat on the water or are you looking for a rabbit in the woods? The larger the object is the easier it is to see. Secondly, are you trying to see details (what we call recognition range) or are you just trying to see if something is there ? Maybe you will see some movement but won’t be able to determine exactly who or what it is. This is called detection range. Another variable is lighting conditions. The more ambient light you have (starlight, moonlight, infrared light) the better and further you will be able to see. You can always see further on a night when the moon and stars are out than if it is cloudy and overcast. We typically state that you can tell the difference between a male and a female or a dog and a deer at about 75 to 100 yards. However, if you were looking across an open field and there was a half moon out you could see a barn or a house 500 yards away. Remember, that the purpose of an NVD is to see in the dark not necessarily a long ways like a binocular.
” Copied with permission from ATN Corporation, ATNCorp.com, Night Owl Optics and Excalibur Electro Optics ”
Data Facts Sheet for Night Vision Devices
What is a System Data Sheet?
A system data sheet is a document that will be included with Gen 3 quality new night vision systems. When deciding on a system, compare the numbers on this sheet to see which system is better. The terms used to compare systems are: photosensitivity, resolution, gain and signal-to-noise ratio. A higher number is better for comparison purposes
What are the definitions of common night vision terms?
GAIN – The number of times a night vision device amplifies light input. Usually measured as tube or system gain, it commonly has values in the tens of thousands. US military image tubes typically operate between 12,000 and 65,000.
LINE PAIRS – a.k.a. line pairs per millimeter (lp/mm). This is a measurement of resolution. The more line pairs, the better the resolution. The best tubes are currently at 64+ line pairs. Generation 3 units will typically have 51 to 64 line pairs and are a factor to consider in price.
PHOTOSENSITIVITY – a.k.a. photocathode sensitivity. It is the ability of the photocathode to produce an electrical response when subjected to lightwaves (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 closer together, measure in line pairs per millimeter (lp/mm). There is a difference between system resolution and image intensifier resolution. System resolution can be affected by altering the objective or eyepiece optics, or by adding magnification lenses. Image intensifier resolution remains constant. System resolution is very important in determining the quality of a system.
SIGNAL-TO-NOISE RATIO – The low light resolution of the image tube. The higher the signal-to-noise ratio, the better the ability of the tube to display objects with good contrast under low light conditions. It is the single best indicator of an image intensifier’s performance.
What are tube blemishes?
Tube blemishes (aka blems or spots) are common in ALL image intensifier tubes. Image tubes are NEVER flawless, and every tube will have blemishes to some degree. The fewer and smaller the blemishes, the better the quality and therefore the higher the price. The best “Grade” of tube would be the Delta Grade, followed by Prime, Prime with Blemish, Choice and Choice with Blemish. Price and line pairs again will determine the quality of the device.