Optical magnification
The degree of image magnification that a night vision device is able to provide without digital image processing, solely due to the optical system. Such an increase is considered to be preferable to digital, because. it does not impair the clarity of the visible image; and for models based on image intensifier tubes (see "How it works"), this is generally the only available option.
Theoretically, the higher the magnification, the greater the detection range (see above), since a powerful increase allows you to see smaller objects. However, it does not always make sense to chase the maximum performance. The fact is that with increasing magnification, the angular field of view decreases and the minimum focus distance increases (see both below), which can create problems at close range. It is also worth noting that a high degree of magnification adversely affects the luminosity of the entire system — as a result, the actual detection range in complete darkness may be higher for a device with a lower magnification, because. it "catches" more light. Yes, and this parameter affects the cost accordingly.
Note that night vision devices, unlike classical binoculars and monoculars, most often have a fixed magnification. Models with the possibility of smooth adjustment are almost never found, and the only option is to use additional nozzles (see "Form factor").
Now on the market are night vision devices with the following optical zoom:
1x,
2 – 3x,
3.1 – 4x,
> 4xReceiver resolution
The resolution of the matrix installed in the thermal imager (see "Type") or digital night vision device (see "Operating principle"). Usually specified in pixels horizontally and vertically, for example 640x480.
On the one hand, the higher the resolution, the clearer and more detailed the image will be. On the other hand, increasing the resolution without changing the matrix size means that less light will fall on each pixel, which negatively affects the detection range (see above) and leads to the appearance of noise. Therefore, the resolution of receivers in modern NVDs is small - in terms of conventional megapixels, it rarely exceeds 0.3 MP. And it hardly makes sense to compare different models by this parameter, because the actual quality of work also largely depends on the size of the receiver, the features of signal processing, etc.
Refresh rate
The frame rate on the screen of the thermal imager (more precisely, on the display visible to the shooter through the eyepiece). The higher this frequency — the smoother and less jerky the image is, the better the thermal imager is suitable for looking at fast moving objects. On the other hand, this indicator directly affects the price of the device and reduces its battery life, because. a high frame rate requires a powerful (and therefore expensive and high consumption) electronic hardware.
Angular field of view
The angle of view provided by a night vision device — that is, the angle between the lines connecting the observer's eye with the two extreme points of visible space. Wide viewing angles allow you to cover a large area, but the magnification factor (see above) is low; in turn, increasing the magnification leads to a decrease in the field of view.
Continuous operating time
The longest time that the device is able to work continuously from fresh batteries without replacing / recharging them. It should be taken into account that manufacturers usually indicate this time for perfect conditions: high-quality batteries, low brightness of the visible image, operation without the use of IR illumination, video output and video recorder (if available, see "Additional"), optimal operating temperature (see below) ) etc. Therefore, in fact, the time of continuous operation may well be lower than stated. Nevertheless, this parameter makes it possible to both evaluate the battery life of individual devices and compare them with each other.
Weight
The total weight of the night vision device in the working position. If a helmet-mask is included in the kit (see above), its weight, usually, is also taken into account.
The large weight of the device makes it inconvenient to use — both when working with hands and when attached to a helmet-mask. On the other hand, with similar characteristics, lighter models will either cost more or have poor quality materials.
