Night Vision Equipment Glossary
Automatic Brightness Control An electronic feature that automatically
reduces voltages to the microchannel plate 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 a constant
Black Spots Usually cosmetic blemishes in the image which are inherent
in the production process. In other cases, as dirt builds on the lens, black
spots are also visible. Black spots resulting from the production process
neither influence the image quality nor interfere with night observation. Spots
which form due to dirt should be removed carefully with a soft cloth.
Bright-Source Protection 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 effect of lowering
resolution when functioning.
- Cycles per Milliradian (cy/mr)
Units used to measure system resolution. A milliradian is
the angle created by 1 yard at a distance of 1,000 yards. This means that a
device that can detect two 1/2-yard objects separated by 1/2 yard at 1,000
yards has a resolution of 1.0 cy/mr. Do not confuse cy/mr with line pair per
millimeter. For example, a system can have a 3X lens attached and increase
the system resolution by a factor of 3, yet the image intensifier's
resolution (measured in lp/mm) has not increased.
Diopter The unit of measure used to define eye correction or the
refractive power of a lens. In most cases, an optical eyepiece will accommodate
for differences in individual eyesight among users.
|Three types of distortion are most
significant to night vision devices: geometric, "S", and
Geometric distortion is inherent in all Gen 0 and
Gen I image intensifiers and in some Gen II image intensifiers that use
electrostatic rather than fiber-optic inversion of the image. 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
S-distortion results from the twisting operation in
manufacturing fiber-optic inverters. Usually S-distortion is very small and
is difficult to detect with the unaided eye, Gen III image tubes
manufactured to U.S. military standards since 1988 have nearly no
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 though the
line were "sheered."
Non-inverting image intensifiers that use microchannel
plates and clear glass for the optics are free of distortion. The image
intensifier ITT manufactures is distortion free.
Electro-optical transducer Primary system which directs and
accelerates the photoelectronic flux taking into account the potential
difference between the photocathode and the screen, and forms the electronic
Emission Point A pinpoint of bright light in the image area that does
not vanish when all light is blocked from the objective lens.
Eye Relief The distance your eyes must be from the farthest element of
an eyepiece in order to achieve the optimal image area.
Gain Sometimes referred to as brightness gain. Gain is the number of
times a night vision device amplifies light input. For a detailed description of
gain and how it can affect performance, please refer to our “First Time Buyer
Infrared Light radiated with wavelengths longer than those of red
Line Pairs per Millimeter (lp/mm) Units used to measure image
Lumen The unit denoting the photons perceivable by the human eye per
Photosensitivity The ability of the photocathode material to produce
an electrical response when subjected to photons.
Recticle The “neon colored” round aiming device found in many
night vision rifle scopes which serves as cross-hairs.
Resolution The ability of an image intensifier or night vision system
to distinguish between objects close together. Image intensifier resolution is
measured in line pairs per millimeter (lp/mm). For a detailed description of
resolution and how it can affect performance