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Night Vision Goggle Techinical Guide (1)

Night Vision Goggle Techinical Guide (1)

1. IIT specs/generation

At present, there are two main types, one is generation 2 +, and the other is generation 3. We usually identify as 2 + and 3, or Gen2 + and gen3.


2. Magnification

Magnification, a numerical value used to represent the relationship between the actual size of an object and its enlarged size. When you look at an object at 700 meters through a telescope with a magnification of 7 times, it is the same size as an object seen with the naked eye at 100 meters. The general magnification includes 1X, 3x, 5x, 6x, 7x, etc.


3. Field of view / FOV

The angle of view takes the lens of the optical instrument as the vertex and the included angle formed by the object image of the measured target passing through the two edges of the maximum range of the lens, which is called the angle of view. The size of the field of view angle determines the field of vision of the optical instrument. The larger the field of view angle, the larger the field of vision and the smaller the optical magnification. The field of view angle is about 40 ° when the monocular binocular night vision instrument is doubled, and it is about 40 ° when the binocular night vision instrument is doubled. At present, the field angle of view of the four-eye night vision instrument under development can reach 80 ° - 120 °.


4. Exit pupil diameter

Exit pupil diameter refers to the diameter of the bright spot formed behind the eyepiece after the light converges through the eyepiece. For optical devices used by the naked eye, light must pass through the pupil and enter the retina for imaging. The pupil of human beings is about 3mm during the day and up to 7mm at night. When observing with optical equipment, the bright spot formed by the light converged by the eyepiece will be projected onto the pupil. Therefore, the larger the exit pupil diameter, the greater the brightness of the image. However, the exit pupil diameter larger than the pupil diameter is meaningless.


5. Exit pupil distance/eye relief

The distance from the apex of the last side 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 whole field of view. In order to avoid the collision between eyelashes and the last side of the system and hinder observation, the exit pupil distance cannot be less than a certain value. For laboratory instruments or ordinary instruments, the minimum exit pupil distance is about 6mm; In military optical instruments, considering the addition of eye masks and gas masks, the exit pupil distance is long, generally about 20mm.


7. Resolution

Resolution is basically a parameter standard to judge the quality of night vision instruments at the same level. Here, there is a premise that the same level. The same level refers to the comparison of night vision instruments belonging to generation 2 + or generation 3. Even the 3rd generation night vision goggles have products with low resolution. There are several levels of medium night vision goggles in each level. The main difference between generation 2 + and generation 3 night vision goggles is the type of cathode tube, while Generation 2 + generally uses S25 and generation 3 uses GaAs. The parameter unit showing the resolution of night vision instrument is LP / mm, which means line pair / mm. The higher this parameter, the higher the resolution of night vision instrument.


8. Diopter adjustment

Diopter, or focal power, is a unit that measures the refractive power of a lens. Diopter adjustment is the key to solve the difference of eye vision. Generally, there are - 6 to + 2, - 5 to + 3, etc.


9. Signal to noise ratio / SNR

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


10. Sensitivity

Sensitivity is also the most important index to describe the brightness of night vision instrument. The higher the sensitivity, the higher the magnification of night vision instrument to 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 are also higher under low light levels. Therefore, the sensitivity reflects the night vision ability of the night vision instrument.