All you have to know about Binoculars and their Application

How to choose binoculars for hunting, fishing, astronomy or sports, and things to keep an eye out for.
This article will help anyone who wants to know more about binoculars. It will disclose the specifications and terms commonly associated with binoculars.
Perhaps the first thing to know is that binoculars are two small mechanically combined telescopes. All the details and mechanics that help us understand telescopes equally apply to binoculars. Each half of the binoculars has a focal length, a lens, an eyepiece, an exit pupil, etc.
The binoculars are designed to allow a person to get a correctly oriented image of a distant object or scene. That is why binoculars are ideal for viewing both ground-based and astronomical objects.


Good binoculars have superior optics and mechanics. Quality is the most important feature of binoculars. A product that is made of high-quality components will stand out, and it always costs more than the popular and widely advertised mediocre models. Quality control comes at a cost to the manufacture (and the buyer), but it's worth it, because the result is binoculars that may well last you a lifetime.

The cost and quality of binoculars is influenced by many different criteria. This includes optical characteristics such as the type of glass used for lenses and prisms, the design of the eyepieces, the size and type of prisms, the level of grinding and polishing of glass elements, as well as the type and coverage of anti-reflective coatings.

Very often, the brand name can serve as a quality mark. Companies like Celestron, Leica, Minolta, Nikon, Pentax, Steiner, Swarovski and Zeiss have earned a reputation in the optical market for decades, and they are unlikely to start producing low-quality products. Other well-known companies, such as Tasco, Jason, and Bushnell, have gained a reputation as manufacturers of affordable optics. Remember, usually you get what you paid for.

It is also of importance which dealer purchased the binoculars. A good dealer can always help you find the binoculars that best suit your needs. Often, good-quality binoculars can be bought in specialized astronomy shops, photo stores, as well as stores that sell hunting and fishing goods.

Unfortunately, many sellers do not possess expansive knowledge about binoculars. Sometimes they even find it difficult to perform basic functions such as focusing the lens. It is always a good idea not to buy optics when the seller cannot provide in-depth information regarding the product. After reading this article you will have a better understanding of how to purchase the right optics and where to find them.

It is worth buying optics from and intelligible and reputable source/store. Good service, however, usually costs a little more. Experienced and knowledgeable sellers deserve higher salaries, and therefore store expenses are higher, which must be partially reimbursed at the expense of buyer. But you must admit, dealing with people who are not trying to sell you the first product they get, and who thoroughly question and select a purchase, is incomparably more pleasant. Good binoculars are an investment for life.



Prisms - this is what allows you to see a correctly oriented image when you look through binoculars. There are two types of commonly used prisms: Porro prisms and roof-shaped prisms.

Roof-shaped prisms are meticulously ordered in optical tubes, and therefore binoculars that have them are more compact. The tubes of these binoculars are usually flat: the diameter of the lens corresponds to the diameter of the eyepiece lens. Such binoculars, due to their compactness, are optimally suitable for athletes. Usually they have two central points between the telescopes, and they are more difficult to adapt to the eye range. Roof-shaped prisms can theoretically help to obtain an image equal in quality to the image with Porro prisms, but for technical reasons this most often does not happen. The higher the cost of the binoculars, the better the image quality with roof-shaped prisms. Do not even try to save on binoculars with similar prisms.

Porro prism binoculars can immediately be identified by heterogeneous telescopes. The lenses inside are usually larger than the lenses of the eyepieces. Front lenses are usually located closer to each other than rear ones, however, in some, especially compact models, the opposite can be true. Optically, the Porro prism design is usually superior to roof-shaped prisms, and this is especially true for mid-range binoculars. The binoculars with the Porro prism have a single center between two tubes, and therefore it is easier to adapt to the interval between the eyes.

Lens Coating

The lenses of most binoculars have an anti-reflective coating. It promotes the transmission of light. It is this coating that produces blue, red or green highlights when you look into the front (objective) lenses of the binoculars.

Pay attention to how the manufacturer describes the coating. “Coated” means a single layer of anti-reflective coating on some lens elements, usually the first and last, that is, those that can be seen. “Fully Coated” means that the coating is applied to all surfaces. Already good. “Multi-Coated” means that at least some surfaces (like the first and last) have a multiple layer of anti-reflective coatings. Such a layer is an order of magnitude more efficient than a single layer. “Fully Multi-Coated” means that multiple layers of anti-reflective coating are applied to all surfaces. It is optimal if your binoculars have this marking.

The most relevant quirks in the field of coatings are ruby or red multi-coatings. They are designed to reduce glare in bright light.



Collimation refers to the optical and mechanical tuning of binoculars. If the binoculars are not collimated, after prolonged use it may seem as if the telescopes are trying to stretch your eyes out of their sockets.

Cheap binoculars often go on sale from the factory without collimation. Good binoculars are collimated by necessity, often with laser tools. This requires time and expense, due to which the cost of the optical device is also increasing.


Increase (Multiplicity)

Usually binoculars are described by a pair of numbers, for example, “7x50” or “8x25”. The first of these numbers means an increase in magnification. It is usually this first number that buyers pay attention to when deciding which binoculars to purchase. For example, the first number 7 in a pair means that the distant object with binoculars will be visible as if it is 7 times closer. Common binocular magnifications are 6x, 7x, 8x, 9x, and 10x.
For example: Nikon Action 7x50 Binoculars

There is also a variable increase (zoom), for example, 7-21x50. At the bottom of the zoom, the binoculars give a better image than the top. This is quite natural, since the lens cannot become larger in order to let in more light, and therefore the larger the zoom, the darker the image. With a seven-fold increase, a lens with a diameter of 50mm forms an exit pupil with a diameter of 7.1 mm, but with a magnification of 21x the exit pupil will be only 2.38 mm, meaning three times smaller.

In addition, the optical quality of binoculars with variable magnification (zoom) is usually lower than that of binoculars with constant magnification. In general, it is best to stay away from the zoom.

Remember that everything increases with binoculars, including movement. The larger the magnification, the more difficult it is to stabilize the remote image. For most people, a magnification of 6 to 8 is optimal, even with trembling or shaky hands. By the way, even army binoculars have a predominantly seven-fold increase.

It is worth remembering one more thing: the increase affects the brightness. All things being equal, the higher the magnification, the darker the image. Also, the increase affects the field of view: the higher the magnification, the smaller the view. When choosing binoculars, it is necessary to take this into account and carefully balance the magnification with other parameters.

Lens Diameter

The second number in the binocular marking indicates the diameter of the lens. In the 7x50 marking, the second number means that the diameter of the objective lens is 50 mm, and this is quite a large value for manual binoculars.

This is especially important information, because the larger the diameter of the lens, the more light gets into the binoculars. That is, ceteris paribus in dim lighting conditions with binoculars with a large lens diameter is better seen. So, 7x50 binoculars are often called night binoculars because it can be clearly seen even in low light. Remember, however, that with a large diameter of the lens, both the dimensions and the mass of the binoculars increase.

Exit Pupil

Magnification and lens diameter determine the size of the exit pupil. The exit pupil diameter determines how much light enters the eye. The exit pupil can be seen holding the binoculars at arm's length and looking through the eyepieces. The beam of light that you see is the exit pupil.

 The actual exit pupil diameter is easy to calculate. To do this, divide the lens diameter by the magnification of the binoculars. For example, turn to the standard size 7x50. Divide 50 by 7 and you get 7.1. So, the diameter of the exit pupil in this case will be 7.1 mm. Take other parameters, for example, 8x25. 25 divided by 8 equals 3.1 mm. Compact binoculars usually always give less light, and the image in them is always darker. When choosing a compact size, we must sacrifice light. For Example:

Olympus 8-16x25 Variable Zoom Binoculars

What is the diameter of the exit pupil? If there is enough light, the pupils of the eyes are much smaller than the exit pupils of the binoculars. But when there is little light, the pupils of the eyes increase, and the static exit pupils of the binoculars can become a limiting factor. Ideally, human eyes in excellent condition can open the pupils up to 7mm, therefore, an exit pupil with a diameter of 3.1 mm will significantly limit visibility in dim light. But in the case of 7x50 binoculars, even in the dark, the eyes fully adapt to the lack of light, and the exit pupil of the binoculars with a diameter of 7.1 mm will not impede the view.

With age, human eyes lose the ability to adapt to the dark, and therefore the maximum pupil size in a middle-aged person usually does not exceed 5mm; in old age - 4mm. Over the years, the smaller size of the exit pupil of the binoculars begins to suit us.

Field of View

The field of view is the area that can be seen through binoculars. As a general rule, it is measured in degrees. The greater the value of the field of view, the larger the area that can be seen. This parameter is especially important for observing moving objects such as animals, birds or athletes in competitions.

Relative Brightness Index (RBI)

The relative brightness index is used to measure the brightness of the image. It is calculated by squaring the exit pupil value. For example, for 7x35 binoculars, the pupil diameter will be 5mm, and RBI = 25.

For Example:
Nikon Action 7x35 Binoculars

An RBI of 25 is considered good for use in low light conditions. Knowing how the value of the exit pupil is calculated and what it means, you can forget about the relative brightness index - the information is by and large superfluous.

Twilight Factor

It will be a question of a somewhat subjective measure, which implies how much detail one can see in twilight conditions (in fact, this is where the name comes from). It is calculated as follows: the lens diameter and magnification (multiplicity) are multiplied, and the square root is extracted from the resulting number. The higher the result, the higher the resolution of the image.

There are some nuances here. For example, the twilight factor influences the sale of binoculars with a large increase, because for 7x50 it will be equal to 18.7, and for 10x50 it is 22.4. However, do not forget about the size of the exit pupil and observation in low light conditions: details are details, but the image should be quite bright.


This parameter was called the twilight factor because it works best when dusk sets in, when the eyes have not yet fully adapted to the dark, and the diameter of the pupils of the eyes is not too large. The twilight factor can be especially useful for a hunter or an ornithologist, since many animals lead a nocturnal lifestyle, and come to life just after dusk.

How to Focus Binoculars

Surprisingly, many people do not know how to properly focus binoculars. There are two common focus systems which are traditionally used.

The first is the individual focusing of the eyepieces. This system is easy to understand and implement. It works well with sealed optical tubes, and therefore is often found in waterproof binoculars. Individual focusing of the eyepieces means that in order to focus the binoculars for your eyes, you need to attach the left eyepiece to the left eye, and the right, respectively, to the right, and adjust each individually, closing eyes in turn. There is no central focusing mechanism.

Since individual focusing of eyepieces is time-consuming, central focusing is more common. Unfortunately, few people understand how to use it correctly. And you need to do the following:

It is necessary to direct the binoculars at a distant object. Close the right eye (or right lens) and use the central mechanism to focus the binoculars on the left telescope. Then close the left eye (or the left lens), and without touching the focusing mechanism, focus the right eye. That is the whole procedure - the focusing process is over.

Binoculars for Travel

Binoculars for travelers should be light and compact so that they fit easily in hand luggage or even in your pocket. Specifically, in this regard a compact type of prism is useful - a roof-shaped one. For the sake of compactness, in this case, you can sacrifice aperture since travelers usually use binoculars in the daytime. The increase (magnification) should be small, from 7 to 10. High optical quality will help compensate for the low aperture.

Binoculars for Astronomy

Good binoculars allow you to see objects in the dead of night, but these should be well-lit objects, such as stars, for example. Once the object is seen through binoculars, it is convenient to point the telescope through it for a more detailed view. The astronomer needs very high-quality and high-aperture binoculars, for example, with parameters such as 7x50, 8x56, and 9x63. In this case, it is advisable to use the maximum number possible, which will assist in trying to avoid shaking the image.

For astronomical needs there are special, often giant binoculars, for example, with parameters of 20x80. To use such an optical device, a tripod is required. For astronomical observations, these are optimal parameters, a compromise between the multiplicity, brightness and field of view.

Binoculars for Hunting and Fishing

To observe objects in the blink of the eye, a sufficiently fast binocular is required. The 7x50 model with an exit pupil diameter of 7.1 is common in the fleet, which means convenience of use by young crew members. Such binoculars also have a good field of view and a sufficient increase (magnification), which is important for observation from a moving vessel. However, such binoculars are quite large and heavy, which is not a problem for some (fisherman, for example). But the hunter needs something more compact.

For hunting in the wild, exit pupils of 4-5mm are usually quite satisfactory, and therefore the most optimal parameters for binoculars for a hunter are 6x30, 7x35, 8x30, or 9x35. All of them are fast enough to see in poor light conditions and compact enough to not overburden the carrier. It is difficult to use binoculars with high magnification without a tripod, and a lens diameter of 40mm or more usually means that the binoculars have considerable weight.

In the forest, a 6x30 binocular with a large field of view is more suitable for a hunter. In the mountains, the advantage is given to a greater multiplicity since you must look for movement at a great distance - 8x30 or 9x35 will be just right. In any hunting conditions, you can do with 7x35 universal binoculars which hare quite powerful and light.

Remember: first and foremost, and the beginning of any binoculars purchase, always prioritize quality. It often costs more but it is always worth it and most likely an investment for life!


Binocular Basics by Chuck Hawks