Eighteen important parameters of night vision devices

(1) Image tube grade/IIT Specs/Generation

There are currently two mainstream categories, one is 2nd generation+ and the other is 3rd generation. The English display is 2+ and 3, or Gen2+ and Gen3. Of course, there are also 4th generation image tubes. The first generation of image tube night vision devices are gradually withdrawing from the market.

(2) Resolution/Resolution

Resolution is basically a parameter standard for judging the quality of night vision devices of the same level. There is a premise here that they are of the same level. The same level refers to comparison among night vision devices belonging to the same generation 2+ or generation 3. Even the 3rd generation night vision devices have products with low resolution, and each level of mid-range night vision devices has several levels of resolution. The main difference between the 2nd generation+ and 3rd generation night vision devices is the type of cathode tube. The 2nd generation+ generally uses S25, while the 3rd generation uses gallium arsenide (GaAs in English). The parameter unit that expresses the resolution of the night vision device is lp/mm, which means line pair/mm. The higher this parameter, the higher the resolution of the night vision device.

(3) Signal-to-noise ratio/SNR

The signal-to-noise ratio is jointly determined by the image intensifier tube and the internal light path of the night vision device. The higher the signal-to-noise ratio, the better the night vision device's ability to prevent external interference in imaging, and the smaller the internal light path interference, so the noise and distortion of the image will be smaller. The image is also clearer. It can also be explained that the signal-to-noise ratio of the 3rd generation is higher than that of the 2nd generation+.

(4) Sensitivity/sensitivity

Sensitivity is also the most important indicator to describe the brightness of a night vision device. The higher the sensitivity, the higher the amplification rate of the night vision device for low-illumination light. Or simply put, the higher the sensitivity, the stronger the brightness of the night vision device, so the brightness and contrast of the image will be higher in low light. So the sensitivity reflects the night vision capability of the night vision device.

(5)FOM value

FOM value, calculated as clarity*signal-to-noise ratio, is used to evaluate the overall performance of night(6) Magnification vision devices. For this parameter, 1000 is the minimum acceptable standard, 1600 is good to use, and 2100+ is pretty great.

(6) Magnification

Magnification is a numerical value that expresses the relationship between the actual size of an object and its magnified size. An object at 700 meters when viewed through a telescope with a magnification of 7x is the same size as an object seen with the naked eye at 100 meters. The magnification of the night vision device when seeing the target, the general magnification is 1X, 3X, 5X, 6X, 7X, etc. At present, most individual night vision devices are 1x and mostly head-mounted, because they are more conducive to the authenticity and reliability of the images viewed. Just imagine if you wear a 5x night vision device on your head, you will not be able to judge the true distance between the target and yourself. High-power night vision devices are generally used handheld.

(7) Field of view (field of view)/FOV (Field of View)

The field of view is also called the field of view. With the lens of the optical instrument as the vertex, the angle formed by the two edges of the maximum range through which the object image of the measured target can pass through the lens is called the field of view angle. The size of the field of view determines the field of view of the optical instrument. The larger the field of view, the larger the field of view and the smaller the optical magnification. The field of view angle of a monocular night vision device at 1x is about 40°, and that of a binocular at 1x is also about 40°. The four-eye night vision device currently under development can have a field of view of 80°-120°.

(8) 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 rays converge through the eyepiece. For optical equipment used with the naked eye, light must pass through the pupil and then enter the retina for imaging. The human pupil is about 3 mm during the day and can reach up to about 7 mm at night. When observing with optical equipment, the bright spot formed by the eyepiece converging light will be projected onto the pupil. Therefore, the larger the exit pupil diameter, the greater the perceived brightness of the image. But an exit pupil diameter larger than the pupil diameter is meaningless.

(9) Exit-pupil distance/Eye Relief

The distance from the vertex of the last surface of the optical system to the intersection of the exit pupil plane and the optical axis. In optical instruments, the pupil of the human eye must coincide with the exit pupil to see the entire field of view. In order to avoid eyelashes from colliding with the last surface of the system and hindering observation , the exit pupil distance cannot be less than a certain value. Laboratory instruments or general ordinary instruments require a minimum exit pupil distance of about 6mm; in military optical instruments, considering the addition of goggles and gas masks, the exit pupil distance is longer, generally about 20mm.

(10) Diopter/Diopter Diopter Adjustment/Diopter Adjustment

Diopter, or power, expressed in English as "Dioptre", is a unit for measuring the refractive power of a lens. Diopter adjustment addresses differences in vision between the eyes. Generally, there are -6 to +2, -5 to +3, etc.

(11) Infrared light/IR Indicator

Nowadays, many 2nd generation + night vision devices and 3rd generation night vision devices are equipped with infrared lights, which are used to enhance the viewing effect at close range at night. Generally, the power is small, and the infrared indicator light (Infrared Illuminator) is built-in, mainly to enhance the concealment when used at night. 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 940 is more concealed, there is no red burst phenomenon or the phenomenon is not obvious, but the effect is not as high as the distance and brightness of the 850.

(12) Low Battery Indicator

As the name suggests, it is an indicator light when the battery power is low. It usually shows a red indicator and is displayed in the eyepiece. The purpose of this design is also to enhance the concealment during use. In addition, the light-blocking eye mask is a soft rubber leather cover at the eyepiece. This eye mask is also used to block the light where the eyes are viewed during use and enhance concealment.

(13) Power Supply/Power Supply

Night vision devices usually use 3V CR123A lithium batteries, which have a long standby time and ensure stable performance of night vision devices. But there are also those that use 1.5V AA alkaline batteries (AA batteries). Of course, there are also two battery types that can support it. For example, there is a binocular monocular low-light night vision device that uses two types of batteries.

(14) Battery life (standby time)/Battery Life

The standby parameters of the night vision device here are written as 40-80 hours, which is a range. The infrared auxiliary light is turned on or not, and the standby time is different. Other brands write 50 hours and some write 60 hours. Everyone writes this parameter in a vague way. It cannot be used as a determining parameter for whether the night vision device meets the customer's parameter requirements. In fact, it can be ignored.

(15) Operating Temperature/Operating Temperature (°C) Storage Temperature/Storage Temperature (°C)

If the customer has no obvious requirements for these two parameters, especially the operating temperature parameter, it is enough to have a rough understanding of these two parameters, which are not rigid parameter indicators of night vision devices.

(16) Focus Range (Range of Focus)/Focus Range (Range of Focus)

Night vision devices are usually 1x, and the focusing range is from 0.25 meters to infinity. The focusing range of most low-light night vision devices is this parameter. However, some brands or manufacturers will set corresponding maximum focus values based on the size of the reference object. For example, the furthest distance for viewing rabbits is 150 meters, the distance for viewing people is 350 meters, and the distance for viewing cars is 500 meters. etc. Reference objects are usually rabbits, people, cars, boats, etc. This parameter is also very flexible, even if the marked distance is a little different from the required distance, it doesn't matter.

(17)Lens System/Lens System

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

What is aperture value? The calculated value of aperture is focal length/clear diameter (that is, lens diameter), which is referred to as F value (also called focal ratio). The larger the F number, the smaller the aperture. On the contrary, the smaller the F number, the larger the aperture. Like traditional cameras, the larger the aperture (the smaller the F value), the better the light transmittance and the clearer and brighter the image.

(18) Environmental level (dustproof and waterproof level)/Environmental Rating

This parameter corresponds to IP + Arabic numerals, such as IP65, IP67, IP68, etc. 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 2nd and 3rd generation night vision devices is IP65, which can also be upgraded to IP68. IP68 is the highest dustproof and waterproof level and can be immersed in 2 meters of water for one hour.

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