 Night-vision Devices FAQs
Some basic rules for caring for night vision
optics include:
- Never turn on your NV optics in daylight with the objective
uncovered.
- Like your eyes, never point your NV optics into a bright light.
- NV scopes can be more sensitive to rough treatment then regular
scopes so avoid rough handling and excessive jolts.
- Always store it in its case.
- Never try to open, alter or fix your NV optics, they are easily
damaged.
- Never replace the batteries without first turning off the IR.
NV optics use high frequency voltage, 15-18 kw!
- Protect the objectives from dampness, dust, sharp fluctuations
of temperature and long exposure to solar radiation (even when
in the case).
- Never touch the objectives.
- Never forget to congratulate it for a job well done.
How do I focus my night vision?
Adjusting night vision devices is the same as adjusting regular
optics. If you have a regular scope most likely it has objective
and eyepiece adjustments. First, adjust the objective lens to
get a better image, then adjust the eyepiece to your eyesight.
If you have binoculars or goggles you have to adjust each eyepiece
separately. To do this close your left eye and make adjustments
to the right eyepiece. Then open you left eye and make adjustment
to the left eyepiece to get a full contrast image. Some night
vision goggles require objective focusing first, and then doing
the eyepiece adjustments. Don't forget that all night vision devices
have a minimal focusing distance, a minimal distance at which
objects can appear in full focus.
How does the night vision work?
Night vision optics use all available light both visible and non-visible
to create an image. Light is gathered by the objective lens and
focused on a photocathode. This cathode emits electrons when exposed
to the light which are then given a high-energy charge by the
power supply. The electrons are accelerated through a vacuum inside
the image intensifier tube and strike a TV-like green phosphor
screen reproducing the image. Since the phosphor screen emits
this light in exactly the same pattern and degrees of intensity
as the light that is collected by the objective lens, the bright
night-time image you see in the eyepiece corresponds precisely
to the outside scene you are viewing. The image is being focused
and magnified by the eyepiece. The phosphor screen is green because
human eye is more sensitive to different shades of green, it is
also the color that contributes the least to eye fatigue.
What do the terms Gen 1, Gen 2 and Gen 3
mean?
Russian and American night vision generations differ significantly.
A general rule of thumb is to add one generation to a Russian
model to find its American equivalent. Thus a Generation 1 Russian
night vision scope would be equal to an American Generation II
scope.
America Gen 1 equipment was originally developed about four decades
ago. Gen 1 night vision equipment is built around image intensifier
tubes with a very simple configuration. A Gen 1 image tube is
vacuum-sealed and consists out of photocathode and a phosphor
screen. Gen1 equipment has lower light amplification (gain) and
image quality (resolution), especially on the edges of the screen.
It typically uses an S-20 photocathode (with photosensitivity
of 180-200mA/lm), electrostatic inversion and electron acceleration
to achieve gain. Because of higher photosensitivity, Gen I was
the first thoroughly passive image intensifier. Gen I is characterized
by geometric distortion, performance at low light levels, and
blooming.
Gen 2 image tubes were developed through the '80s, and differ
from Gen 1 tubes by utilizing a micro-channel plate (MCP). MCP
looks like a honeycomb where each cell has a large number of channels
for electrons to enter. It is located between the photocathode
and the phosphor screen. For each accelerated electron emitted
by the photocathode that strikes the channels of the MCP, about
1000 electrons come out on the other end and hit the phosphor
TV-like screen. MCP boosts light gain of an image tube by about
1000 times. As a result the output image is brighter. It usually
uses an S-20 (extended red) photocathode (with photosensitivity
of 240+mA/lm) and microchannel plate to achieve gain. They come
with either electrostatic or fiber-optic inversion and provide
good performance at low light levels and exhibit low distortion.
Gen 2 equipment is costly and fits the needs of more advanced
users. It is widely used for tactical and professional surveillance
purpose.
Gen 3 equipment is very similar to Gen 2 by its use of MCP, but
in addition, it uses a Gallium Arsenide (GaAs) photocathode, which
is more light sensitive. As a result more electrons are emitted
to hit the MCP and then the image screen to produce a brighter
image. Gen 3 equipment is the latest night vision technology.
Gen 3 equipment yields best results when used in poorly lit environments
such as canyon, forest or jungle. If most of your surveillance
is in urban or nearby areas, Gen 2/2+ equipment will do an excellent
job. The microchannel plate in Gen III is coated with an ion barrier
film to increase tube life. Gen III produces more then 800mA/lm
in the 450 to 950 nanometer (near-infrared) region of the spectrum.
Gen III provides very good to excellent low-light-level performance,
long tube life. Recent mil-spec quality tubes have no perceptible
distortion.
Automatic Brightness Control (ABC).
An electronic feature that automatically reduces voltages
to the microchannel plate (2nd & 3rd Gen) of the intensifier
tube to keep the image intensifier's brightness within optimal
limits and protect the tube. The effect of this can be seen when
rapidly changing from low-light to high-light conditions the image
gets brighter and then, after a momentary delay, suddenly dims
to constant level. This can be an issue with the flash of a gun.
Black Spots.
These are cosmetic blemishes in the image intensifier or can
be dirt or debris between the lenses. Black spots that are in
the image intensifier do not affect the performance or reliability
of a night vision device and some number of varying size are inherent
in the manufacturing processes. Spots due to dirt or debris between
the lenses should be removed by careful cleaning if the system
is designed for interchanging optics.
Bright-Source Protection (BSP).
An electronic function that reduces the voltage to the photocathode
(usually 1st Gen) 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 effect of lowering resolution when functioning.
Distortion.
Three types of distortion are most significant to night vision
devices: geometric, "S" and sheer.
Geometric Distortion.
This basic distortion is inherent in all Gen I image intensifiers
and in some Gen II image intensifiers that use electrostatic rather
than fiber-optic inversion of the image. Russian night vision
optics do not use fiber-optic inversion and thus are superior
to Western night vision optics that do. Geometric distortion is
eliminated in image tubes that use a microchannel plate and fiber-optics
for image inversion, however, some S-distortion can occur in these
tubes.
S-Distortion.
S-distortion results from the twisting operation in manufacturing
fiber-optic inserters (fiber optic twister - Russian tubes do
not use a fiber optic twister). Usually S-Distortion is very small
and is difficult to detect with the unaided eye. Gen III tubes
manufactured to U.S. military standards since 1988 have nearly
no perceptible S-Distortion.
Sheer Distortion.
Sheer distortion can occur in any image tube that uses fiber-optic
bundles for the phosphor screen. It appears as a cleavage or dislocation
in a straight line viewed in the image area as through the line
were sheered. Non-inverting image intensifiers that use microchannel
plates and clear glass for the optics are free of distortion.
The 2nd Gen. image intensifiers that Russians make are distortion
free, since they do not have fiber-optics twisters.
Equivalent Background Illumination (EBI).
EBI is the amount you light you see in an image tube that
is turned on but there is no light at all on the photocathode;
it is affected by temperature where the warmer night-vision device,
the brighter the background illumination. EBI is measured in lumens
per square centimeter (lm/cm2) and the lower the value the better.
The EBI level determines the lowest light level at which you can
detect something. Below this light level, objects will be masked
by the EBI.
Eye Relief.
The distance your eyes must be from the last element of the
eyepiece in order to achieve the optimal image area. Longer eye
relief allows you to see the full field of view at a greater distance
from the eyepiece and is ideal for eyeglass wearers and forward
and pistol mounts.
Fixed Pattern Noise (FPN).
A faint hexagonal (honeycomb) pattern throughout the image
area that most often occurs under high-light conditions. This
pattern is inherent in the structure of the microchannel plate
and can be seen in virtually all Gen II and Gen III systems if
the light level is high enough.
Gain.
Also called brightness gain or luminance gain. This is the
number of times a night vision device amplifies light input. It
is usually measured as tube gain or system gain. Tube gain is
measured as the light output divided by the light input. This
figure is usually seen in values of tens of thousands. If tube
gain is pushed too high, the tube will be "noisier"
and the signal-to-noise ratio may go down. On the other hand system
gain is measured as light output divided by the light input and
is what the user actually sees. System gain is usually seen in
the thousands. In any night vision device, the tube gain is reduced
by the system's lenses and is affected by the quality of the optics
or any filters, therefore, system gain is a more important measurement
to the user.
Gallium Arsenide (GaAs).
The semiconductor material used in manufacturing of the Gen
III photocathode. GaAs photocathodes have a very high photosensitivity
in the spectral region of about 450 to 950 nanometers (visible
and near-infrared region).
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. Electrons entering a channel strike
the wall and knock off additional electrons which in turn knock
off more electrons producing a cascading effect. MCP's eliminate
the distortion characteristic of Gen 0 and Gen I systems. The
number of holes in an MCP is a major factor in determining resolution.
Photocathode.
The input surface to an image intensifier that absorbs light
energy and in turn releases electrical energy in the form of an
electron image. The type of material used in a distinguishing
characteristic of the different generations of image intensifiers.
Photosensitivity.
Also called photocathode sensitivity. The ability of the photocathode
material to produce an electrical response when subjected to light
waves (photons). Usually measured in micro-amps of current per
lumen of light. The higher the value the better the ability to
produce a visible image under darker conditions.
How Far Can You See.
There many different variables that can affect the distance
that you can see with a Night Vision Device. Obviously, the larger
the object, the easier it is to see. Lightning conditions also
play a big role. 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 where the moon and stars
are out then if it is cloudy and overcast. Typically 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.
Photocathode Response (photosensitivity).
The ability of the image tube to detect light under very dark
conditions and convert that low light level into an image that
you can see is gauged by its photosensitivity. The higher the
numerical value, the better the ability to produce a visible image
under darker conditions.
Resolution.
Resolution is the ability of the tube to distinguish between
objects. The higher the numerical value, the better the tube will
distinguish between objects. An image tube_s resolution is measured
in line pairs per millimeter (lp/mm).
Signal-to-Noise Ratio.
Is the computed ratio of measured data from photosensitivity,
gain, and resolution. The higher the ratio, the better the ability
of the tube to produce a clear image under very dark conditions.
What is Infrared (IR) Illuminator and do
I really need one?
An Infrared Illuminator or simply IR, is a source of infrared
light which is invisible to the human eye. Roughly, it is a flashlight
emitting infrared light instead of a visible white/yellow light.
It is used to increase available light for brighter images. Most
of the IR illuminators on the consumers' market are based on LED,
a Light Emitting Diode, similar to your TV's remote control. Many
of our regular scopes come with an IR to give better performance
in dawn and dusk conditions.
What is the effective viewing range of the
Night Vision Device?
It varies anywhere from 300 to 1500 feet. The viewing distance
depends on the area, conditions and a size of your target. Overcast
conditions, fog, rain and snow will significantly reduce the effective
viewing range. On the other hand your viewing range will increase
dramatically under clear skies and/or full moon. Light reflective
surfaces such as snow or sand will also increase the effective
viewing range of your night vision device. An Infrared illuminator
(IR) may help, especially in enclosed environments.
Can I use night vision in complete darkness?
It is possible to use NVDs in complete darkness with the help
of an IR Illuminator. Since most of the time you encounter complete
darkness in enclosed environments, high magnification power is
not a necessity, you'd rather be able to see at a very close range.
In this case the most effective viewing device is a goggle. Most
goggles have magnification power of 1, built-in IR Illuminator,
close focus and a viewing range of a few hundred feet.
Can a Night Vision device and/or Infrared
Illuminator be harmful?
Night vision technology is absolutely harmless, it doesn't
emit radiation nor will it blind you if a bright light hits it
while in use. Most likely it will damage the device. Night vision
is no more dangerous or harmful than watching TV. Diode (LED)
based IR Illuminators are also harmless.
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