How to choose binoculars


Binoculars are a simple and useful technical tool that allows you to observe distant objects. Their fundamental structure has not changed for a long time, the set of characteristics is small, but at the same time, there is not much sensible information about how to choose binoculars. Therefore, we decided to write this article.

Binoculars with porro prisms

So who are binoculars for?

In fact, for many users. The fact is that with any exit to the city and nature, we see a lot of distant objects that would be interesting to consider in detail. What is good binoculars in this case? It gives a stereoscopic image, 3D, as it is now fashionable to say, unlike, for example, a camera lens.

There are budget models of binoculars, so if you don’t know for sure whether you need it or not, there will be something to try. Although, of course, to anyone who has used binoculars or looked through them in a store, the difference in image quality between different price categories will be obvious.

First, let’s look at the basic devices of binoculars.

So, binoculars can be divided into several main parts:

  1. Eyepieces – the back of the binoculars, facing the eye of the observer.
  2. Objectives – part of the optical system, facing the observed object.
  3. focus mechanism. There are binoculars with central and separate focusing.
  4. With central focusing, control is carried out by a wheel in the central part of the binoculars – adjustment is carried out immediately for both eyes.

    Binoculars with central focus

    With separate – focusing is carried out separately for each eye.

    Binoculars with split focus

  5. Mechanism of diopter correction. Not available if there are separate focusing mechanisms for each eye.

Between different binoculars there may be fundamental differences in the internal structure. The two most common types are:

  1. Binoculars with Galilean tubes – the optical design consists of only two optical elements – one in the lens and one in the eyepiece. The simplest scheme, which, however, does not allow to achieve a large increase.

  2. Binoculars with Galileo’s pipes

  3. Prismatic:
    1. Binoculars with Porro prisms – due to total internal reflection in two prisms, the light changes direction four times, each time by 90 degrees. A characteristic feature is the different distance between the centers of the objective lenses and eyepieces.
    2. The most common option is when the lenses are at a greater distance, which increases the stereo effect:

      Porro prism binoculars with classic layout

      However, in compact models, the option is common when the distance between the lenses is less.

      Olympus 10×25 PCI binoculars – with Porro prisms and compact layout

      Porro prisms in binoculars are used in cases where maximum performance is required at a minimum cost. Their only drawback is that with a large lens diameter, the binoculars turn out to be wide and massive.

    3. Binoculars with roof prisms.

    4. Binoculars Olympus 10×42 Exwp I – binoculars with roof prisms

      In them, the distance between the centers of the lenses of the eyepiece and the objective is the same, so that the binoculars are more convenient and lighter, but more expensive to manufacture, compared to Porro-prism ones. Also, the disadvantage is that for layout reasons it is impossible to create binoculars with large objective diameters (the limitation arises due to the impossibility of increasing the distance between their optical centers).

So, knowing the fundamental structure of binoculars, we can talk about its technical characteristics. There are not many of them, but all of them are very important:

  1. Magnification (multiplicity) is the main and most important characteristic. Determines how many times the linear dimensions of the object of observation in binoculars will be larger than those visible to the naked eye.
  2. The diameter of the front lens element is the second most important characteristic. The magnification and diameter of the front lens are indicated in the specifications of the binoculars through the multiplication sign: 8×42 – where the first number is the magnification, and the second is the diameter of the front lens in millimeters.
  3. The exit pupil diameter is equal to the ratio of the diameter of the front lens to the magnification of the binoculars. The exit pupil is nothing more than a circle of light, which is formed, for example, on a sheet of paper, if you bring a binocular lens to it. The diameter of the exit pupil affects the so-called luminosity of binoculars, that is, its ability to form an image bright enough to observe an image in low-light conditions. According to this characteristic, binoculars are conditionally divided into:
    • Binoculars with a small aperture – the exit pupil is less than 3 mm.
    • Medium aperture – 3-4.5mm.
    • Aperture – 4.5-6 mm.
    • High aperture – over 6mm.
  4. However, it should be understood that increasing the diameter of the exit pupil above a certain value does not make sense. The fact is that if it turns out to be larger than the diameter of the pupil of the observer’s eye, then the “extra” part of the light beam is simply lost.

  5. Transparency coefficient – indicates how much of the light that enters the lens passes through the optical system of the device. For example, a transparency factor of 0.7 indicates that the binoculars will transmit 70% of the light.
  6. The minimum focusing distance is the minimum distance at which binoculars can be focused with focus adjustment.
  7. The angle of the field of view of binoculars – as the name implies – is the angle in degrees in the horizontal plane, the top of which is the center of the binocular lens, and the sides are the lines that limit the field of view.
  8. Removal of the exit pupil (working distance) – the distance between the exit pupil and its projection on the rear lens of the binocular eyepiece. In essence, it means the minimum distance that you can bring your eye to the rear lens when using binoculars. Determines the convenience and ability to use binoculars with glasses.
  9. The presence of moisture protection, water resistance, filling with neutral gas – determine the ability of the binoculars to work without breakage at high humidity and temperature changes. Important for those types of binoculars that are used in nature.
  10. The presence of a stabilizer. An optical stabilizer is a device that has appeared in binoculars quite recently. It compensates for image shaking that occurs when handheld binoculars are used.
  11. Goniometric grid – is present in some specialized models and is used, as a rule, to measure the distance to the observed object.

Of course, in addition to design features, binoculars differ in purpose. Here are the following types:

  1. Tourist. These are lightweight, rubber-coated, and often water-resistant binoculars with above-average magnification designed for nature observation.

  2. Binoculars Nikon Sportstar EX 8×25 DCF

  3. Hunting. Classic binoculars with medium magnification, camouflage coloring and a fairly wide field of view, but medium in size. Designed to search and observe animals.

  4. Binoculars Nikon Monarch 3 8×42

  5. Theatrical. Binoculars with Galilean tubes, low magnification and a special elegant design. The design may include a pen – lorgnette.

  6. Theatrical binoculars Veber Opera BGC 3×25 with lorgnette

  7. Baby. Light and simple binoculars in bright colors, designed for children.

  8. Children’s binoculars

  9. Astronomical – binoculars with high magnification, massive design, designed to be mounted on a tripod. For example, galaxies and nebulae can already be observed with 25x binoculars.

  10. astronomical binoculars

  11. Marine – must have high image quality, decent magnification and resistance to aggressive conditions for a long time. A characteristic feature here is the presence of a compass, which is extremely important in order to determine the bearing of an object observed at sea.

  12. marine binoculars

General recommendations

So, as always, when choosing binoculars, you should decide what it will be used for.

It should also be said that chasing the maximum magnification is not worth it: at high magnification, the field of view of the binoculars will decrease, and hand-held observation will become more difficult due to image shaking. It should be mentioned that binoculars with high magnification can even come with an adapter for a tripod.

It is also worth paying attention to the warranty period of the binoculars: it speaks about the overall quality of the device, its durability.

Convenience and everything connected with it is also of considerable importance: a rubberized case, controls, weight, equipment, and so on. For example, it would be extremely useful if the device comes with a case or a case with a carrying strap.

On sale you can find binoculars that do not require focusing, and this is presented as a virtue. However, if you look at this more closely, you can understand that this is not the case. For example, some primitive cameras also do not require focusing (webcams, mobile phone cameras). This only means that they have low image quality and aperture ratio. It is the same with binoculars: fixed focus binoculars have poor image quality, a dark image and do not give a clear image at close range.

The same problem, albeit to a lesser extent, occurs with zoom binoculars: they are more versatile, but not suitable for those who need maximum image quality and aperture. This is because with a variable magnification, the design of binoculars becomes more complicated, the number of optical elements increases.


Binoculars can be used for different tasks, and, accordingly, have different characteristics. But, in general, the types of these devices that are popular with ordinary users are tourist, hunting, theater binoculars and general purpose binoculars. Armed with the knowledge from our article and coming to the store, it will not be difficult to choose them.

As for children’s binoculars, here it is necessary to take into account the opinion of the future user, and in the case of astronomical and marine ones, separate articles can be written.

And, of course, you should buy binoculars only in trusted stores.


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