| Night vision technology enables you to see
objects clearly at night at distances of up to several hundred yards in the absence of any
artificial light. People, buildings, vehicles and details of the landscape viewed
through a modern night vision system appear almost as if illuminated while the same
objects viewed with a naked eye would appear only as indistinct shadows (or won't be
visible at all).
In order to understand how any night vision devise works compare it to a
video camera but a very special one, with an extremely high sensitivity to light.
All night vision systems provide the viewer with electronically enhanced
viewing. When you use a night vision scope, you are not actually viewing the scene
before you, but instead you are viewing a video image of that scene. The heart of
any night vision system is an image intensifier tube.
The intensifiers are rated as either first, second or third generation.
Image intensifier tubes basically consist of a PHOTOCATHODE which converts light
images to electron images (these, in turn can be amplified); and a microchannel plate (in
the 2nd and 3rd generations), which converts the flow of electrons back to a light image.
The FIRST GENERATION image intensifier tubes, or GEN 1as they are known
uses simple grid shaped electrodes to accelerate the electrons through the tube. The
SECOND and THIRD GENERATIONS of tubes (GEN 2 and GEN 3) use complex MCP (MICROCHANNEL
PLATES) that not only accelerate the electrons pulled from the photocathode, but increase
their number. This increased charge then causes the phosphors to glow more
brightly in response to the light reflected.
As a result one can see more light at the viewing end of a second or
third generation tube for a given light level. Second and third generation
tubes also generally exceed first generation tubes in their ability to resolve detail,
eliminate image distortions and they have longer useful tube life.
Night Vision products are available in variety of forms including,
binoculars, hand held viewers, goggles, telescopes and rifle mounted scopes. Some of
them are camera and/or video adaptable as well.
Sierra Pacific Innovations brings you top superpower nightvision
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NIGHT VISION TERMINOLOGY
Automatic Brightness Control (ABC) - An
electronic feature that automatically reduces voltage to the microchannel plate to keep
the image intensifier's brightness within optimal limits and protect the tube. As
the result of this image would get brighter and then, after a momentary delay, suddenly
dim to a constant level during the rapidly changing conditions from low-light to
high-light.
They can also be dirt or debris between the lenses which should be
removed by careful cleaning if the system designed with interchangeable optics.
Bright - Source Protection (BSP) - An electronic
function that reduces the voltage to the photocathode when the night vision device is
exposed to bright light sources such as room lights or car lights. BSP protects the
image tube from damage and enhances its life; however, it also has the disadvantage of
lowering resolution when functioning.
Diopter - The unit of measure used to define eye
correction or the refractive power of a lens. Usually adjustments to an optical
eyepiece accommodates for differences in individual eyesight. Usually ranges from +5
to -5.
Eye Relief - The distance your eyes must be from
the last element of an eyepiece in order to achieve the optimal image.
Generation 0 - Typically uses an S-1
photocathode with peek responses in the blue-green region (with photosensitivity of 60
mA/Im), electrostatic inversion, and electron acceleration to achieve gain.
Consequently, Gen 0 tubes are characterized by the presence of geometric distortion and
need for active infrared illumination.
Generation I -
Typically uses an S-20 photocathode (with photosensitivity of 180 - 200 mA/Im),
electrostatic inversion, and electron acceleration to achieve gain. Consequently,
Gen I was the first passive image intensifier. Gen I is characterized by
geometric distortion, weak performance at low light levels, and blooming. Expected
lifespan is 1500 hours.
Generation II -
Usually an S-25 (extended red) photocathode (with photosensitivity of 240 + mA/Im and a
microchannel plate to achieve gain). Can be found with either electrostatic or
fiber-optic inversion. Gen II tubes provide satisfactory performance at low light
levels and exhibit low distortion. Expected lifespan is 2500 hours.
Generation III -
Uses gallium-arsenide for the photocathode and microchannel plate for gain. The
microchannel plate is also coated with an ion barrier film to increase tube life.
Produces more than 800 mA/Im in the 450 to 950 manometer (near infrared) region of the
spectrum. Gen III provides very good to excellent low-light -level performance, long
tube life. Expected lifespan is 10,000 hours.
Most consumers feel that a night vision device wont last long based on
the tube lifespan, but in reality, if a night vision device is being operated for 100
hours per YEAR, then this is considered A LOT of useage. At 100 hours per year a gen 2
device would last for 25 years and a gen 3 device would last 100 years.
Microchannel Plate (MCP)
- A metal-coated glass disk that multiplies the electrons produced by the
photocathode. An MCP is found only in Gen II and Gen III systems. These
devices normally have anywhere from 2 to 6 million holes (or channels) in them. MCPs
eliminate the distortion characteristic of Gen 0 and Gen I systems. The number of
holes in the MCP is a major factor in determining resolution.
Photocathode - The
input wavelengths of the intensifier that absorbs light energy and in turn releases energy
in the form of an electron image. The type of material used is a distinguishing
characteristic of the different generations of image intensifiers.
Click
here to see how THERMAL INFRARED IMAGING works
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