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What are the parameters of a night vision device?

Image tube rating /IIT Specs/Generation

At present, there are two mainstream categories, one is 2 generation +, and the other is 3 generation. Or, it is 2+ and 3, or Gen2+ and Gen3.

Magnification /Magnification

Magnification is a numerical value that represents the relationship between the actual size of an object and its enlarged size. Observing an object at 700 meters through a telescope with a magnification of 7 times is the same size as seeing a thing with the naked eye at 100 meters. The magnification of the night vision device when it sees the target, the general magnification is 1X, 3X, 5X, 6X, 7X, etc.

Field of View (FOV)/Field of View (FOV)

The Angle of view, also known as the field of view, takes the lens of the optical instrument as the apex, and the Angle formed by the two edges of the maximum range of the object image of the measured target through the lens is called the Angle of view. The size of the field of view Angle determines the field of view of the optical instrument, the larger the field of view Angle, the larger the field of view, the smaller the optical magnification. In the case of a monocular night vision device, the lot of view Angle is about 40°, and the binocular binocular is also about 40°. The four-eye night vision currently under development has a field of view Angle of 80°-120°.

Exit pupil diameter /Exit pupil diameter

The exit pupil diameter refers to the diameter of the bright spot formed behind the eyepiece after the light converges through the eyepiece. For the optical equipment the naked eye uses, the light must enter the retina after the pupil, the human pupil is about 3 mm during the day, and the maximum can reach about 7 mm at night. When viewing with optical equipment, the bright spot formed by the convergence of light from the eyepiece will be projected onto the pupil, so the larger the diameter of the exit pupil, the greater the image’s brightness. But the exit pupil diameter larger than the pupil diameter is meaningless.

Exit pupil distance/ exit-pupil distance/Eye Relief

From the vertex of the last side of the optical system to the intersection point of the exit pupil plane and the optical axis, in the optical instrument, the pupil of the human eye must coincide with the exit pupil to see the entire field of view, in order to avoid eyelashes and the east side of the system to interfere with the observation, the exit pupil distance can not be less than a certain value. Laboratory instruments or general instruments require a minimum exit pupil distance of about 6mm; In military optical instruments, considering the addition of an eye mask and a gas mask, the exit pupil distance is longer, generally about 20mm.

Resolution /Resolution

Resolution is basically a parameter standard to judge the quality of the same level of night vision, and there is a premise that it is the same level. The same level refers to the comparison of night vision devices belonging to Generation 2 + or Generation 3. Even the third generation of night vision equipment also has low-resolution products, and each level of night vision resolution has several levels. Then the main difference between the 2 generation + and the 3 generation night vision device is the different types of cathode tube, the 2 generation + generally uses S25, and the 3 generation uses gallium arsenide (English is GaAs). The parameter unit of night vision resolution is lp/mm, meaning line pair /mm, the higher the parameter, the higher the resolution of night vision.

Diopter Adjustment /Diopter adjustment

Dioptre, or focal power, in English “dioptre”, is a measure of the refractive power of a lens. Diopter adjustment is used to resolve differences in eye vision.

In general, there are -6 to +2, -5 to +3, etc.

Signal-to-noise ratio /SNR

The signal-to-noise ratio is determined jointly by the image enhancement tube and the internal light path of the night vision instrument. The higher the signal-to-noise ratio, the greater the external anti-interference ability of the night vision instrument imaging, and the smaller the internal light path interference, so the noise and distortion of the imaging are smaller and the imaging is clearer. It can also be explained that the signal-to-noise ratio of generation 3 is higher than that of generation 2 +.


Sensitivity is also the most important indicator to describe the brightness of the night vision instrument, the higher the sensitivity, the higher the magnification of the night vision instrument for low illumination. Or simply put, the higher the sensitivity, the stronger the brightness of the night vision device, so in low light, the brightness and contrast of the image are also higher. So the sensitivity reflects the night vision ability of the night vision device.

Infrared light /IR Indicator

Now many of the 2 + generation night vision and 3 generation night vision devices themselves are equipped with infrared lights, the effect is to enhance the viewing effect at night. Generally, the Infrared Illuminator is low power, and the infrared illuminator is built-in, mainly to enhance the invisibility of night use. At present, there are generally two common infrared wavelengths, one is 850nm (nanometer), and the other is 940nm. The difference between the two infrared is that the concealment of 940 is stronger, there is no red explosion phenomenon or the phenomenon is not obvious, but the effect is not as high as the distance and brightness of 850.

Low Battery Indicator

As the name suggests, it is the indicator light when the battery is low, which generally shows a red indication and is displayed in the eyepiece. The purpose of this design is also to enhance the concealment when used. In addition, the blackout eye mask is a soft rubber leather cover at the eyepiece, so the eye mask is also used to cover the light of the place where the eyes are watching when using and enhance the use of concealment.

Power Supply

Night vision equipment is usually used more is the 3V CR123A type lithium battery, this battery is long standby and ensures the stable performance of night vision equipment. However, there are also 1.5V AA alkaline batteries (No.5 batteries). Of course, there are also two battery types that can support this, such as DG2051.

Battery Life (standby) /Battery Life

The standby parameters of our night vision device are written to be 40-80 hours, which is a range, and the standby time is different when the infrared auxiliary light is turned on or not turned on. There are other brands that write 50 hours, and there are 60 hours. This parameter is very vague. It can not be used as a decision parameter whether the night vision device meets the customer’s parameter requirements. In fact, it can be ignored.

Operating Temperature (°C)

If the customer has no obvious requirements for these two parameters, especially the operating temperature parameters, the two parameters can be roughly understood, not a hard night vision parameter index.

Focus Range (Range of Focus)

Night vision devices are usually 1 time, the focus range is from 0.25 meters to infinity, and the focus range of most low-light night vision devices is this parameter. However, some brands or manufacturers of the focus range will be based on the size of the reference object and set the corresponding focusing maximum value, for example, the distance to watch the rabbit is 150 meters, the distance to watch the person is 350 meters, the distance of the car is 500 meters and so on. The objects of reference are usually rabbits, people, cars, boats and the like. This parameter is also very flexible, even if the distance specified is a little different from the required distance.

Lens System

This parameter is usually composed of two parts: aperture value and lens aperture. For example, F1.2, 25mm. F1.2 is the aperture value and 25mm is the lens aperture.

What is the aperture value? The aperture is calculated as the focal length/light diameter (that is, the lens aperture), referred to as the F-number (also known as the focal ratio). The larger the F-number, the smaller the aperture. Conversely, the smaller the F-number, the larger the aperture. As with traditional cameras, the larger the aperture (the smaller the F-number), the better the transmittance, and the clearer and brighter the image. Lens system This parameter can also be customized according to the requirements.

Environmental Rating (dustproof and waterproof rating)

This parameter corresponds to IP+ Arabic digits, such as IP65, IP67, and IP68. The first number 6 refers to the dustproof level, and the second number 5 refers to the waterproof level. The following is a further explanation of the performance represented by specific numbers. The default dustproof and waterproof level of Dongdi 2 and 3-generation night vision is IP65, and can also be upgraded to IP68, IP68 is the highest dustproof and waterproof level and can be soaked in 2 meters of water for an hour. If you need to upgrade to IP68, the cost will increase by 2000 yuan.

FOM value

First, you need to know some important parameters that describe night vision:

Resolution unit lp/mm, meaning line pair /mm. The higher the parameter, the higher the resolution of the night vision device. For this parameter, 51 is an acceptable minimum, 64 is good to use, and 72 is pretty good

The parameter signal-to-noise ratio (S/N), which describes the low-light performance of the night vision instrument, has no unit. The higher the noise of the night vision instrument in low-light conditions, the less noise and the clearer the image. For this parameter, 20 is an acceptable minimum, 25 is good to use, and 30+ is pretty good

The parameter photocathode sensitivity describing the brightness of the night vision instrument is μA/lm, which means microampere per lumen. The higher the parameter, the brighter the night vision instrument is in the dark environment, and the higher the parameter, the higher the gain of the night vision instrument. For this parameter, 700 is an acceptable minimum standard, and 2000+ is fine

FOM value, calculated as resolution * signal-to-noise ratio, is used to evaluate the comprehensive performance of night vision equipment. For this parameter, 1000 is an acceptable minimum, 1600 is good to use, and 2100+ is pretty good

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