The characteristics of binoculars, monocular and telescope, the size of the exit pupil, relative brightness, twilight factor and magnification, their influence on the quality of observation.

Undoubtedly, a sniper should be distinguished by exceptional accuracy, but even the best shooter will not be able to shoot without finding a target, and most sniper targets are intentionally hidden. The sniper team spends a quarter or even a third of the time on the mission, observing the terrain with binoculars, a measuring tube monocular, and an endless search for an elusive target. 

Characteristics of binoculars, monocular and telescope, size of the exit pupil, relative brightness, twilight factor and magnification, their influence on the quality of observation.

Observation of the terrain requires as much accuracy and attention to detail as firing at hitting a target at a great distance, and it all starts with the realization of the need to study the amazing terrain mosaic.

Advantages of optical instruments, binoculars, monocular and telescope over the naked eye.

The hand-held telescope, created by the Dutch eyewear maker Hans Lippershey in 1608, was a revolutionary breakthrough in 17th century military affairs, akin to decryption machines or spy satellites in our time.

Imagine the enormous tactical advantage that a frigate captain gained by raising his spyglass to his eyes and he could detect enemy ships at such a distance that even the most careful observer could not see them. This gave a significant advantage in battle and was actively used. The Dutch government deemed it necessary to keep Lippersheye’s invention, which helped “see at a great distance”, a secret.

The optical equipment of a modern sniper team, if applied correctly, is no less important than during the sailing battles. Optics allows you to perform the main task of a sniper – to “see while remaining invisible”, both when detecting a target and when conducting reconnaissance by observation.

The characteristics of binoculars, monocular and telescope, the size of the exit pupil, relative brightness, twilight factor and magnification, their influence on the quality of observation.

The advantages of optics over the naked eye are undeniable. I once gave a demonstration to my students. He planted a cadet with optics at a distance of 1 mile from the group, without any shelter. Even the most keen cadets could not see him, and he described on the radio my smallest movements. The demonstration impressed the cadets, since we were behind a line of trees and should not have seen us.

I would also like to impress you, since observation includes a number of related skills, such as detecting a target, evaluating a detected target for value and importance, observing fire and adjusting sniper shots. It is necessary not only to find something, but to understand what you have found, to help the sniper to see it, to help him adjust the direction of the fire to hit the target.

The size of the light spot or the size of the exit pupil of the binoculars, monocular and telescope.

Your eye is the channel through which all images enter your brain. To be more precise, light enters the eye through the pupil. A hole that acts like a camera lens. In low light, the pupil expands in order to distinguish less distinct forms, and narrows in bright light in order to protect sensitive nerve tissue.

The most effective optical devices convert the collected light into an image of the same diameter as the pupil of your eye. That is, the beam of light from the sight or binoculars should be of the same diameter as the pupil of the eye of the observer. This is easy to achieve in daylight, because the diameter of the pupil is about 3 mm. Almost any binocular or telescope is suitable for this task..

However, at dusk and at night, the pupil expands, in order to let in more light and many optical devices are not able to create a light spot of the same diameter as the pupil, that is, 6-7 mm. Despite the fact that you may not notice this defect, it depends on what a person sees in poor lighting.

Therefore, the light spot size of the device — or “exit pupil size” —is an important criterion that is easy to calculate. To do this, divide the diameter of the objective lens by the magnification that they give. For example, binoculars 7&# 215; 35 exit pupil size 5 mm, and the sight 20&# 215; 60 – 3 mm.

Relative brightness and twilight factor, as important characteristics of binoculars, monoculars and telescopes.

Another parameter for evaluating optical devices is called “relative brightness”, when calculating which it is necessary to square the size of the exit pupil so that the difference becomes algebraic, and the advantages are more noticeable, as shown in the table below.

The characteristics of binoculars, monocular and telescope, the size of the exit pupil, relative brightness, twilight factor and magnification, their influence on the quality of observation.

The third way to measure and evaluate the passage of light is the “twilight factor”. It adds significance to the multiplicity of the device in low light conditions, and thus emphasizes the ability to distinguish details at dusk and in moonlight. This criterion is very important for the sniper team. However, for a reliable comparison of devices, only the twilight factor of the two devices should be compared with similar values ​​of the exit pupil diameter. Otherwise it makes no sense.

To calculate the twilight factor, multiply the lens diameter of the device’s lens by the lens power. Then calculate the square root of the result. Since binoculars have 7&# 215; 35 and 10&# 215; 50 the size of the exit pupil is 5 mm, let’s compare their twilight factor and determine which one will be more useful when observing at dusk:

7&# 215; 35 = 245, square root – 15.6 = twilight factor
10&# 215; 50 = 500, square root – 22.4 = twilight factor

Therefore, the binoculars 10&# 215; 50 twilight factor significantly higher. Somehow, representatives of law enforcement agencies called me asking what binoculars to use to monitor drug dealers in the evening, 7&# 215; 35 or 10&# 215; 50, and I think it’s clear to you why I recommended the second option. However, I also asked the officer if he was going to conduct surveillance from cover or to act undercover, since the binoculars 10&# 215; 50 is harder and harder to hide than 7&# 215; 35.

When choosing optics, one should be guided not only by the parameters of the device. My favorite binoculars for observing and searching for targets, Steiner Night Hunters 8×56 mm, has an impressive twilight factor of 21.1. This value is higher with binoculars. 15&# 215; 80, however, they are a third heavier and twice as bulky.

There will be those who do not agree with my choice of Night Hunters binoculars, since it is heavier than binoculars 7&# 215; 50 and has not the same magnification as binoculars 10&# 215; 50. Like everything in life, the choice of optics is based on compromises, and not just on its numerical characteristics.

The importance of choosing quality binoculars, monoculars and telescopes.

Before considering various parameters – the size of the exit pupil, relative brightness or twilight factor – remember that they will not tell you anything about the quality of the lenses. They will tell only about their size or multiplicity. Poorly polished third-grade glass cannot become the basis of high-quality optics, despite all its indicators.

High-quality lenses require precise polishing and a microscopic coating that will allow light to pass through them unhindered, without distortion and glare – the glass should be more transparent than crystal. Only high-quality lenses allow you to observe from a long distance.

Do not be fooled by large lenses. Perhaps they will collect a large amount of light, but if the device is not made of high quality, then only a small amount of it will reach your eyes. The same applies to high multiplicity – if the focused image is too vague, and you can’t see the person pointing the rifle at you, then who needs this power?

High-quality optics often seem expensive, but they justify the cost. If you can’t get the best optics, try to get the best quality possible. Since saving on optics for the sniper team is extremely unwise.

Selection of magnification of binoculars, monocular and spyglass.

How powerful should your optics be? If the multiplicity is 10x – that’s good, will not 50x be better and 500x even better? Do not fall into the misconception that the greater the multiplicity, the better. The more powerful the optics, the larger it is in size and weight and the more limited its scope.

In addition, the multiplicity of optics is inversely proportional to its field of view. The more powerful the device, the more limited the area that you can observe with it. It is precisely because of the limited visibility and the too distant minimum focal length that the astronomical telescope should not be used for observation by substitution.

Another important limiting factor is mirage. Due to interference from the glare of warm air currents, using optics with a magnification of more than 30x will cause problems. As for the optical sights, the maximum magnification at which the mirage does not significantly affect the clarity of the image is about 12x.

The upper limit of the magnification for binoculars depends on how physically possible it is to hold it motionless. With a fixed position of the body, you can clearly see distant objects with binoculars with a magnification of 10x or 12x. A person is not able to hold still a more powerful device and therefore, the visible image will be distorted.

If the team uses a telescope and binoculars, the binoculars can be relatively light: 7x or 8x. However, if there is no pipe, the team will need binoculars with at least 10x magnification. Since with its help they will not only conduct surveillance, but also adjust the sniper fire. Ideally, the team should have several complementary appliances.

Based on the book “The Perfect Sniper. Study Guide for Army and Police Snipers ».
Maj. John L. Plaster, USAR (Ret.)

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