We’ve all seen movies in which some form of a soldier and special forces troops are attacking an enemy at night using a night vision scope. We’re familiar with the green tinted camera work that signifies night vision. We know what it looks like, but how does it work?
Night vision enhances the image you see by amplifying the existing light and allowing the user to see infrared light. Infrared light is invisible to the naked eye and requires the use of special devices to see. The amplification of this light makes it possible to essentially see in the dark.
Night Vision Scope Considerations
When you are looking into purchasing some form of night vision or another there are certain considerations you should consider. These conditions change depending on your budget, your intended use, and the features you require. Today, we are going to talk specifically about night vision scopes.
The ergonomics of a scope are much different than the ergonomics of other night vision devices. When using a night vision scope you need an optic with easy to use controls. You need to be able to control all functions of the optic from behind a rifle. You’ll need to be able to increase the zoom, turn it on and off, use an IR illuminator, and adjust the optic for clarity all from behind the rifle. In most shooting situations, lighter is better. A heavy optic will make a rifle difficult to shoot, and straining to even hold steady. So remember, weight is important when choosing an optic of any kind.
Clarity in a night vision scope is critical. A scope is often used to spot a specific target. If you can’t tell what you’re looking at you can’t identify your target. Clarity or resolution is measured by lines per millimeter when it comes to night vision. The higher clarity you have, the more millimeters per line your night vision scope will have. When attempting to determine the clarity of an optic, look for the following acronym, LP/MM. (LP = Lines Per / MM = Millimeter.) For example, the militaries PVS 14s has 64 to 72 LP/MM.
Distortion can affect the clarity of an LP/MM rating. Distortion is mainly caused by the materials used to make the lenses. High-quality lenses will be made from glass, and present less distortion. Optics that use poor quality glass or even plastic lenses will have a greater level of distortion. Distortion is also more common in older generations of night vision, due to a lack of an MCP. Generation 2 and above will rarely have serious distortion. Gen 2 and up have mostly minimal geometric distortions. At longer ranges, this distortions can increase and make a target indecipherable. Your LP/MM is your overall clarity rating but is not the final clarity rating.
Signal to Noise Ratio
When looking through night vision, or even seeing it on TV, you’ve seen the ‘snow’ effect it has. This ‘snow’ is called noise. Signal is the light signal that your eye actually perceives. Signal to noise measures is the amount of signal that reaches your eyes divided by the noise. So signal to noise is a more measured and refined clarity. The higher the signal to ratio is, the clearer the optic will be.
Night vision devices require some form of light to function. Night vision does not produce light, it merely amplifies it. The more ambient light the clearer and farther you can see. Gain is what is required to see clearer and farther with a night vision device. Gain is also known as luminance gain. Gain is measured in tube gain and system gain. Tube gain is often in the tens of thousands and system gain in the several thousand. Tube gain is dependent upon the lenses. Too high of a tube gain and you increase the noise seen. System gain is light output divided by light input. System gain is the most important measurement.
Field Of View
Field of view is measured at a particular magnification at 100 yards. Field of view decreases as magnification increases. For example field of view at 2x in a night vision scopes maybe 30 feet from one side of the lens to the other, but at 8x the fov maybe only 14 feet. A wide field of view gives you a greater view of an area in front of you. Night vision scopes often have an effect known as blooming around the edge of the field of view. This decreases the overall field of view partially.
Night Vision Generations
Night vision is split into 4 distinct generations. You can argue five, but Gen 0 are rare antiques that are no longer sold. Night vision generations create the biggest differences in the price of night vision scopes.
Gen 1 – The earliest mass produced models used in the Vietnam war. These optics need moon or starlight to function correctly. Without some form of ambient light, this generation is close difficult to use. THere are Generation 1+ devices that function extremely well with less light.
Gen 2 – Gen 2 night vision scopes saw a massive increase in clarity and usefulness and a large drop in size. These optics are capable of working in very little light. Generation 2 optics are still proficient enough to be used for shooting and scouting.
Gen 3 – Generation 3 night vision scopes increased the clarity of night vision devices, but remained the same overall size. There was a sharp decrease in the amount of necessary light required to use these optics efficiently. These optics are the current military and police issue in most cases.
Gen 4 – Generation 4 improved clarity by up to 20 percent by removing the protective coating around the microchannel plate. This also decreased the overall lifespan of generation 4 night vision scopes. Gen 4 optics are rare and extremely expensive when found. The lowered lifespan and increased cost have prevented these scopes from being popular.
It’s no secret night vision is an expensive technology. The more you know about it, is the more you understand it. The more you understand, the better investment you will make. Read, learn, and take careful considerations when buying a night vision scope.