Understanding the technology of night vision devices
Article by Cobus Cronje
Understanding how night vision works is absolutely essential before considering to buy such a device.
In this article you will be introduced to topics like “amplification of light”, “infrared illuminator” and “phosphor screen”. Once you’ve familiarized yourself with these concepts, you will understand how night vision works.
There are basically four types of night vision devices, being binoculars, monoculars, scopes and finally goggles. Only the first two types will be discussed. As far as technology is concerned, I will focus only on Generation 1 technology. The other technologies (2-4) are not suited for recreational purposes.
The fundamental purpose of a night vision instrument : Making it possible for the viewer to see things at night – that’s what they are for; not for magnifying objects and making them look closer, like binoculars can do (although some of them do have a weak magnification).
Seeing at night is only possible if some light is available. Like coming from the stars or the moon, or from some artificial source. This is then utilized by the device and amplified and Voila! You can see a raccoon move in the bush, whereas you will only see darkness with your bare eyes!
Sometimes you wish you had 10,000 times more light, for you’re missing something huge going on in the dark. Even the amplifying ability of your night sight device is not good enough – apparently there’s simply not enough light available: No moon, no stars. If only your device had an infrared (IR) illuminator! (You could have bought a supplementary one in any case, but you though your instrument would be good enough.) Never buy a night vision device without an IR illuminator. This is a must. With this your light can be improved by 15,000 to 40,000 times, enabling you to see what you like in the dark.
Phosphor screen: The image that you see is actually not the physical object itself, but a projected, amplified electronic image on a phosphor screen (like a green, monochrome TV screen), which glows with a green colour. This is perfect, since the human eye can distinguish more shades of green than any other colour.The eyepiece then magnifies the image for you to see. You cannot see in colour with a night vision device.
Limited life warning: Binoculars, telescopes, scopes and monoculars can last for an indefinite time as long as you take good care of them, but night vision devices have a limited lifetime. The phosphor screen can perform for 1500 hours of use up to 2500 hour, which is an awful lot of time. Then the screen has had it and the instrument has become useless. But that should not prevent you from buying one! The pleasure you will get using one will be very rewarding. On top of this the lifetime of the screen could be shortened dramatically if not used as intended. These instruments have extremely sensitive light components. These will be damaged when used during daytime or exposed to overloads of lights like flashlights or spotlights. All in all it means that you should not buy a used one – unless you know exactly how the previous owner had used it.
Flaws in the image tube: The image tube of a night vision device can never be perfect and flaws have an impact on the quality of the image presented to the viewer. These flaws are black spots scattered over the image area. The better quality the instrument (equals higher price), the less the black spots and the lesser the quality, the more black spots. You can also get a slight distortion of the edges of images.
Summary: A night vision instrument is a complicated piece of technology; you have to use it as intended to avoid damage to the sensitive electronics. It is not an instrument which enables you to view far away objects as if close to you; it’s made for viewing objects at night when no human being can do that. To make this possible, the little light available at night is enhanced and supplemented by an infrared illuminator and the image is projected onto a phosphoric screen. In the case of a night vision device price does make a difference; the more expensive, the better the images you look at; cheaper instruments have some black spots and slight distortions at the edges of the images. All in all, this instrument will provide a lot of pleasure for a long time.
About the Author
Cobus Cronje has also written on pocket binoculars (www.pocketbinoculars.net).
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