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A night vision monocular is an optics device which allows people to see in dimly lit conditions. Like other night vision optics, night vision monoculars compensate for poor human vision at night, allowing people to essentially see in the dark. Night vision monoculars can be used for a variety of purposes, including hunting and making observations of wildlife populations, but many are utilized in military applications. The most sophisticated systems are reserved for military and police use, but some very excellent versions are available to civilians who are willing to pay a premium price.
The design of a night vision monocular can be passive or active. In a passive system, the lens opening is very wide, gathering as much light as possible before passing through a series of lenses which intensify the light before it reaches the eye. The scene usually acquires a greenish tint when viewed through a night vision monocular because of the filtration lenses used.
In an active system, the device scans for infrared signatures, and then displays an image of the landscape. In highly advanced systems which are capable of detecting subtle differences, the picture can be extremely crisp and clear, making it highly useful. In simpler systems, the user sees blotches of color coded by intensity, which can identify people, animals, engines, and other hot spots in the landscape which may be relevant to the user's activities. Passive systems are not just capable of seeing in the dark. They can also be used to see in obscured visual conditions like fires and sandstorms.
As the term “monocular” would suggest, a night vision monocular has a single lens assembly, instead of two. This design can create a flattened effect and distort perspective, which is something to be aware of when using a night vision monocular. Depending on the design, the device may only be used by one eye, or it may feed an image to both eyes. One advantage of the monocular design is that it has the capability to be much smaller than night vision binoculars, making it more portable. The lens opening can also be extremely wide, increasing the image quality, because the design doesn't need to accommodate two lens assemblies.
Night vision monoculars can be found in use as rifle sights, and in head-mounted assemblies, in addition to being hand held items. Science stores and military surplus stores are often a good source for night vision monoculars, which should ideally be tested before purchase to ensure that they will meet the needs of the user. Some stores have darkened rooms designed specifically for this purpose, or photographs demonstrating the level of night vision available in optimal conditions.