Comparison Yukon Exelon 4x50 vs Pulsar Challenger GS 2.7x50

The greatest distance at which a night vision device is capable of detecting individual objects.

The methods by which manufacturers determine this parameter may vary in detail, but the general principle is the same. Usually, the distance is indicated at which, with an illumination of 0.05 lux (a quarter of the moon) and a medium-contrast background, a rather large object can be seen — for example, a human figure with a height of about 170 cm is most often taken. of this object, but only to notice the very fact of its presence. Simply put, a detection range of, say, 200 m means that “something that looks like a person” can be seen in such a device at a distance of 200 m, but individual parts (head, hands) cannot be disassembled.

It is also worth noting that in fact this parameter is highly dependent on the characteristics of the situation. For example, a dark object on a very light background will be visible further, and on a dark one it may not be noticeable even up close; a similar phenomenon is observed for thermal imagers (see "Type"), only regarding the difference in temperature, and not in colours.

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, > 4x

The focal length of a night vision device. This term means such a distance from the optical centre of the lens to the photocathode of the image intensifier tube or the matrix of a digital device(see "Operation principle"), at which a clear image is obtained on the photocathode/matrix.

In general, long focal lengths are characteristic of optical systems with a high degree of optical magnification (see above). However, in the case of night vision devices, this dependence is not rigid — it is simply easier to ensure a high magnification with long-focus optics. In fact, this means that models with the same focal length can differ markedly in magnification. But what this indicator directly affects is light transmission: other things being equal, longer optical systems transmit less light, which negatively affects the capabilities of the device. This is also true for thermal imagers (see "Type"), because their working infrared range in this case also obeys the general laws of optics.

The resolution of the visible image created by the night vision device. Indicated by the number of lines (strokes) per millimetre; the higher this indicator, the more detailed the image is capable of creating the night vision device, the better small details will be visible on it. However such devices will cost accordingly.

In models with an image intensifier tube (see "How it works"), the resolution is highly dependent on the generation of the transducer.

The size of the area visible in the night vision device from a distance of 100 m — in other words, the largest distance between two points at which they can be seen simultaneously from this distance. It is also called "linear field of view". Along with the angular field of view (see below), this parameter characterizes the space covered by the optics; at the same time, it more clearly describes the capabilities of a particular model than data on viewing angles.

The smallest distance to the observed object, at which it will be clearly visible through the night vision device. For normal use of night vision devices, it is necessary that this distance does not exceed the minimum expected distance to the objects in question; thus, it must be borne in mind that the higher the magnification factor (see above), the greater the focus distance, usually.

The diameter of the exit pupil created by the optical system of a night vision device. The exit pupil is called the projection of the front lens of the lens, built by optics and electronics in the region of the eyepiece; this image can be observed in the form of a characteristic light circle, if you look into the eyepiece not close, but from a distance of 30 – 40 cm.

The practical significance of this parameter is that for normal visibility it must be no less than the size of the pupil of a person looking into the eyepiece. The diameter of the human pupil can vary from 2-3 mm in bright light to 7-8 mm in the dark. Therefore, the larger the size of the exit pupil of the night vision device, the better the visibility, usually; this is especially true with a minimum amount of light, when the brightness of the image is low even when viewed through the device. On the other hand, this feature significantly affects the cost of the device.

The offset is the distance between the eyepiece lens and the exit pupil of an optical instrument (see "Exit Pupil Diameter"). Optimum image quality is achieved when the exit pupil is projected directly into the observer's eye; so from a practical point of view, offset is the distance from the eye to the eyepiece lens that provides the best visibility and does not darken the edges (vignetting). A large offset is especially important if the night vision device is supposed to be used simultaneously with glasses — after all, in such cases it is not possible to bring the eyepiece close to the eye. It is also relevant for devices that can be installed on a weapon: the greater the distance to the eye, the less likely it is to get injured due to recoil.

The wavelength of infrared radiation emitted by the IR illuminator installed in the night vision device. In most cases, this parameter is purely reference: manufacturers usually select the wavelength in such a way that it best suits the features of the device and provides the claimed characteristics. Nevertheless, a practical moment is also associated with the wavelength — the "visibility" or "invisibility" of the illuminator (see "Invisible radiation spectrum").