Detection range
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.
Continuous zoom
The ability to adjust the degree of magnification within a certain range, allowing you to adapt the night vision device to different conditions and situations. Thus, when observing over long distances, it is optimal to use a higher magnification to obtain a detailed image. And when moving or observing in low visibility conditions, zooming out may be preferable to expand the field of view. Night vision devices with
variable optical magnification are universal and adaptable tools, however, such a function is extremely rare - most often NVGs have a fixed magnification (see “Optical magnification”).
Field of view at 100 m
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.
Exit pupil diameter
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.
Operating temperature range
Ambient air temperature range at which the night vision device will be guaranteed to maintain normal performance. This indicator is very important, given that such devices are most often used outdoors, where the temperature variation can be very large. Of course, when choosing, you should take into account the conditions in which you plan to work with the device — for example, it hardly makes sense to specifically look for a frost-resistant model for hunting in the summer. But in general, the wider the operating range, the higher the overall reliability of the device, the less sensitive it is to adverse climates.
It is worth noting that going beyond operating temperatures does not necessarily lead to instant failure; however, even with the preservation of operability, the probability of failure increases many times, and such cases are not covered by the manufacturer's warranty.
