Binoculars – a Device for Observation

Introduction

Binoculars are one of the most important pieces of hunting equipment. Without them, the inspection of the game is virtually impossible. For an ethical shot, they are a must-have. In some cases, an experienced shooter can use a hunting rifle without a riflescope, but for a detailed evaluation of the game, which encompasses an estimation of the animal’s age, gender, and size, binoculars are an indispensable accessory, regardless of the hunter’s experience. Even though almost every hunter is aware of the advantages that binoculars bring, the knowledge on binoculars, in general, is still lacking. In the continuation of this article, we will discuss some terms connected with the use of binoculars. Furthermore, we will describe what separates one type of binoculars from the other. We will deliberately skip the parts associated with optical characteristics which separate top-notch binoculars from mediocre ones, as a separate article will be written on that topic. The purpose of this article is to highlight the differences between individual types of binoculars, elaborate on their physical characteristics and classify them according to the fields of use.

Magnification

In the configuration of the binoculars, which is often listed in their names, there are two crucial pieces of information – the magnification and the diameter of the objective lens. 8×42 binoculars, for example, offer 8x magnification and 42mm objective lenses. When we look through one of these, we see objects magnified 8 times in comparison to the naked eye observation. With other words, if we use binoculars with 8x magnification to observe objects 80 m away, they will be of the same size as if we were looking at objects 10 m away with the naked eye. It all comes down to the user preference with magnification choice. Most users go for magnification between 7x and 10x. In this zone, an average individual can hold the binoculars in their hands without the shaking of hands having a noticeable impact on the observing experience. Because of the issues with shaking, some people prefer 8x magnification to 10x – lower the magnification, the less noticeable the shaking.

On the left side, a view through a binocular with an 8x magnification can be seen; on the right side, there is a view through a 10x magnification binocular

On the left side, a view through a binocular with an 8x magnification can be seen; on the right side, there is a view through a 10x magnification binocular

Lens diameter

This is the second piece of information that is listed in the names of binoculars. It is a highly important parameter since it is associated with the amount of light that comes into the optical system. People tend to link bigger objective lenses to a brighter image, but this can only be applied to the binoculars of a specific manufacturer that belong to the same series. Premium binoculars with a 42mm objective lens can, for example, provide a brighter image than binoculars with a 56mm objective lens of low quality. Two crucial pieces of information listed in the binoculars’ names (magnification and objective lens diameter) let the user know the width of the beam of light that enters the user’s eye during observation. The density of the light beam, however, is dependent on other parameters, such as the quantity and quality of the coatings, applied to the optical components. The objective lens diameter also affects the binoculars’ weight. If you are looking for light binoculars, the pocket type is a great choice, but the image will not be as bright when it starts to get dusky. It is important to determine which parameters you need most and make a purchase based on that.

Exit pupil

The exit pupil is a diameter of the beam of light that exits the eyepiece of the binoculars and enters the user’s eye. It’s a geometrical value that can be calculated by dividing the diameter of the objective lens with the optical device’s magnification. 8×42 binoculars thus have an exit pupil of 5.25 mm (42 / 8 = 5.25). The average person’s pupil can dilate to around 7 mm. Because of this, manufacturers produce binoculars with an exit pupil up to this value. The dilation capabilities of our pupils are affected by age. The older we are, the smaller the size to which our pupils can dilate. Our pupils tend to dilate to their maximum size in the dusk. During the daytime, our pupils measure around 3 mm in diameter, meaning that all the binoculars with an exit pupil above 3 mm will provide an equally bright image. 8×30 binoculars with a 3.75mm exit pupil are, for example, equally bright during daytime observations as 8×56 binoculars with a 7mm exit pupil – in both cases, our pupils will only allow a beam with a diameter of around 3 mm to reach the receptors in the eye (during daytime, our pupils are usually no bigger than that). We can see that exit pupil is of negligible importance during the day but extremely important for observations in the dusk. 8×56 binoculars will provide a much brighter image during twilight observations compared to 8×30 binoculars because of their astounding 7mm exit pupil. Since the human’s eye can dilate to 7 mm in youth only, many users cannot benefit from the bigger lens when they are older. This is the main reason why there are more 42mm objective lens binoculars on the market.

Prism types (Schmidt-Pechan, Abbe-Koenig, Porro)

All the modern binoculars have in their construction an optical element called prism. Prism’s job is to refract the beam of light that passes through the optical system several times. By implementing prisms in binoculars, optics manufacturers achieve two important things. Firstly, the size of the binoculars is greatly reduced. Secondly, a prism rotates the image of the observed object so that we do not perceive it as turned on its head (the lenses are responsible for turning the image upside down). On the market, three types of prisms are the most common. Abbe–Koenig and Schmidt–Pechan prisms are of the roof type. They are named after their shape which resembles a roof. Porro prisms, named after their inventor Ignazio Porro, are a little bit different. Prisms are one of the most important components found in binoculars, which is why the characteristics of both types will be elaborated on in paragraphs that follow.

On the left side, there is a binocular with a Porro prism and a focusing system for each eye individually; on the right side, there is a binocular with a Schmidt and Pechan prism and a central focusing system

On the left side, there is a binocular with a Porro prism and a focusing system for each eye individually; on the right side, there is a binocular with a Schmidt and Pechan prism and a central focusing system

Binoculars that have Porro prisms inside can be easily recognized because of their unique shape – the objective lens is not aligned with the ocular lens. A few decades ago, binoculars with these prisms were extremely popular. Gradually, they were superseded by binoculars with roof prisms. The most notable advantage of binoculars with Porro prisms is that there is a lower number of refractions of the beam of light compared to the binoculars with roof prisms. Because of this, a high light transmission rate and a brighter image can be achieved. Furthermore, the prisms have highly reflective surfaces. The downside of these binoculars is their size – they are large and clumsy. Manufacturers also tend to have more problems achieving waterproofness with Porro binoculars than with roof binoculars.

Nowadays, roof prism binoculars are the most popular. They are divided into two subgroups – binoculars with Abbe–Koenig prisms and binoculars with Schmidt–Pechan prisms. The latter comprise approximately 95 % of the roof prism binoculars manufactured. The construction of Schmidt–Pechan prisms allows for a very compact binocular construction and a low mass. The surfaces of these prisms are not as reflective as those on Porro prisms, and the beam of light gets refracted more times, which is why roof prism binoculars generally offer a lower light transmission rate than Porro binoculars. To achieve a high light transmission rate, manufacturers make use of several coatings which they have at their disposal. This is the main reason why high-quality roof prism binoculars are so expensive. With the development in the field of optical coatings, manufacturers are now capable of producing roof prism binoculars with a top-notch edge-to-edge sharpness and impressive colour fidelity. Even though manufacturers constantly upgrade their Schmidt–Pechan roof prism binoculars, they still cannot be equated with Abbe–Koenig and Porro prism binoculars when it comes to the light transmission rate.

Abbe–Koenig prism is, like the Schmidt–Pechan prism, of the roof type. Not many manufacturers produce binoculars with these prisms since they are extremely difficult to make. Because the manufacturing process is so strenuous, binoculars with these prisms carry a high price tag. These binoculars boast an incredible light transmission rate that is comparable to that of Porro prism binoculars. Abbe–Koenig prisms provide great sharpness, impressive colour fidelity, and a high light transmission rate. For now, only two manufacturers are bold enough to manufacture binoculars with this prism type.

From left to right: Porro prism, Abbe-Koenig prism, Schmidt-Pechan prism. From the picture, it is apparent that Abbe-Koenig binoculars are longer than those with Schmidt-Pechan prisms, even though both are categorized as roof prisms

From left to right: Porro prism, Abbe-Koenig prism, Schmidt-Pechan prism. From the picture, it is apparent that Abbe-Koenig binoculars are longer than those with Schmidt-Pechan prisms, even though both are categorized as roof prisms

Eyepieces

The eyepieces are, interestingly, scarcely listed as a crucial part of a binocular. It is important that we keep an eye out for some important factors. The eye has to be positioned around 15 mm behind the eyepiece to see a proper image, which is why having a proper eye relief is of great importance. Those who use glasses must keep the eyecups turned inwards, while those who do not wear them must set an eyecup position that suits them most. Most contemporary binoculars offer three or four eyecup positions, some premium binoculars offering 5 or even more. In practice, binoculars which offer greater eye relief tend to be more convenient for use. Porro binoculars have some problems with eye relief because the eyecups can usually only be set to two positions (the rubber on the eyepieces can be rolled inwards or left in place). It is thus important that glasses wearers and people with astigmatism try out a Porro binocular before buying it just to make sure that they can conveniently use it. Roof prism binoculars are more comfortable to use since they usually offer 3, 4 or even more eyecup positions. This allows the users to set the eye relief so that it perfectly corresponds with their vision.

In the upper line, three different eyecup positions can be observed; in the lower line, Porro binoculars' eyecups can be observed (bottom left picture - one single setting on a Porro binocular, difficult to use with glasses ; bottom right picture - multi-stop eyecup on a Porro binoculars, can be used with glasses as well)

In the upper line, three different eyecup positions can be observed; in the lower line, Porro binoculars’ eyecups can be observed (bottom left picture – one single setting on a Porro binocular, difficult to use with glasses; bottom right picture – multi-stop eyecup on a Porro binoculars, can be used with glasses as well)

Focusing systems and the dioptre setting

Almost exclusively, roof prism and Porro prism binoculars are equipped with a central focusing knob. This configuration provides great accuracy and the capability of focusing the image at very close distances one from the other. A small percentage of binoculars lacks the central focusing knob – on these binoculars, the focusing is done for each eye individually. With these, the focus is set only once. The user’s eyes then focus on the observed object, regardless of how far away it is. This type of binoculars is advantageous in low light conditions where one might find the use of a central focusing knob problematic – the lack of light prevents the user to determine when the image is in focus. Secondly, the user does not have to set the dioptre for any of the eyes. With a central focusing knob binocular, the dioptre is usually on the right eyepiece. To set it correctly, the user must close the right eye, set focus on a specific distance with the central focusing knob, close the left eye, set the dioptre so that the observed object is in full focus. Once this is set, the focusing is done solely with the central focusing knob (unless someone else uses the binoculars). Binoculars that lack the central focusing knob have one notable disadvantage – usually, it is difficult to observe objects at close distances, such as 25 m away. Because of this, binoculars with the central focusing knob are much more popular than the ones that lack it.

Twilight factor, relative brightness, and light transmission rate

In the past, coatings were not yet used on binoculars, meaning that all the optics manufacturers were technologically somewhere on the same level. During this period, optics enthusiasts used several terms when comparing one binocular to another. Today, some of these are obsolete, but many manufacturers still list them in the specification table. One of such is the twilight factor. To find out the twilight factor the user must multiply the product’s magnification with the diameter of its objective lens and then calculate the square root of the product. For example, the twilight factor of the 8×42 binoculars is 18.33. All the 8×42 binoculars boast an 18.33 twilight factor. In the past, this would mean that all the 8×42 binoculars produce an equally bright image. Today, there are plenty of coatings available, one different from the other, meaning that the twilight factor is no longer a useful piece of information. Relative brightness is another obsolete term. It is calculated by squaring the value of the exit pupil. It was once a useful piece of information but today, the use of various technologies has rendered it obsolete. Nowadays, technologies used, the quality of material and choice of applied coatings define the optical quality of binoculars. Even the term ‘light transmission rate’ is not as established as it once was since some manufacturers use unacclaimed measurements to achieve the results. Furthermore, the value that manufacturers list under ‘light transmission rate’ can in some cases be influenced by internal glare which raises the value by a few percents during measurements but has no effect on producing a brighter image in practice. In short, geometrical values used in the field of binoculars in the past are completely useless for establishing their quality nowadays.

On the left side, a focusing system for each eye individually can be seen; on the right side, a central focusing system can be seen

On the left side, a focusing system for each eye individually can be seen; on the right side, a central focusing system can be seen

Field of view

This piece of information is still highly important. In the field of binoculars, the value provided under the ‘field of view’ refers to the area seen when observing objects 1000 m away. Sometimes, the value is expressed in minutes of angle, with the help of which the metric value can be calculated. In general, better binoculars provide a wider field of view than low-quality, cheap binoculars. The binoculars from the ‘cream of the crop’ category are distinguished from one another based on the edge-to-edge sharpness. In general, there is a belief that a bigger field of view is better, even though the edge sharpness might be compromised.

Binoculars' field of view

Binoculars’ field of view

Lens materials and coatings

Low-quality binoculars are distinguished from high-quality ones based on the materials used for construction. This means that high-quality binoculars feature quality glass, and multicoated lenses and prisms. On the more expensive ones, meticulous craftsmanship can be noticed when paying attention to details. In the last decade, optics manufacturers are flaunting by putting several abbreviations next to their products’ names. The most commonly used ones are HD, ED, BAK4, FL, and Ultra. These usually refer to the type of glass used. This is a marketing move – it does not necessarily imply that the binoculars are of excellent quality. The evolution of glass in the field of optics had three major turning points in the last few decades. The first one was the development of glass with a high density (at the beginning, this was marked with ED). It was followed by the introduction of glass with fluoride and the presentation of glass with a higher light transmission rate. The last two innovations are nowadays widely used by the three premium European optics manufacturers. As regards the coatings applied to the optical components, there are even more abbreviations in existence than with the glass type. Premium optics manufacturers use their own technologies and the manufacturing process of many is kept secret. The coatings used are one of the most important parts of a binocular – with a top-notch coating, the light transmission rate can be enhanced, better colour fidelity achieved, and sharpness improved. In other words, the coatings used are what separates the crème de la crème from average. The binoculars of the highest quality have multi-layer coatings on all the lens and prism surfaces, to which optics manufacturers refer as ‘Fully-Multicoated’. The coatings, applied on the external parts of the lenses, are also gaining in popularity. These are used to prevent external fogging which occurs when a person exhales onto the lens. A coating of this type is especially useful during winter. Partially, these coatings also protect the surfaces from abrasion, dust and other particles. The coatings are usually copyrighted by the manufacturers – these come up with intriguing names for them: AquaDura, Rainguard, LotuTec, Swarodur, etc.

Filled with dry nitrogen, argon

Old binoculars used to have problems with internal fogging at low temperatures. Furthermore, they were not waterproof, and the interior was filled with air. Because air contains some moisture, a temperature difference between the air inside the binoculars and the air outside resulted in condensation on the internal parts of the lenses. Optics manufacturers solved this problem by filling the binoculars with dry nitrogen or argon. Neither of these two gases contains moisture. Furthermore, they have no effect on the optical characteristics of the device.

Electronic components (rangefinder, compass, image stabilizing)

The development in the field of electronics has brought about several changes, even in binoculars. A few devices of this type are equipped with a rangefinder, compass, or an image stabilizer. The last two are almost exclusively limited to marine use, while rangefinder is an accessory that hunters are fond of, particularly when making long shots. Some binoculars with an integrated rangefinder also provide the user with a ballistics calculator – the user can input the ballistic data of his or her ammunition. The calculator usually proposes three different types of correction of the point of impact. 1. The user is given a mark to which he or she must move the center of the reticle. 2. The user is told of the number of clicks that must be dialed on the ballistic turret 3. The user is told of the number of clicks that must be dialed on the traditional turret. Currently, only the most expensive binoculars with an integrated laser rangefinder provide this enviable feature. Furthermore, only the highest-quality rangefinder binoculars do not have impaired optics because of the laser system (the tint in one of the tubes is a common issue). If you are looking for mid-range binoculars, and the rangefinder is not a must-have for you, it is still better to purchase standard binoculars from the same price level as they will provide you with a far better optical experience.

Conclusion

In this article, we have discussed the most common terms associated with the field of binoculars. Its purpose is providing valuable information for all binocular users out there (hunters, birdwatchers, etc.)

To help hunters decide what binoculars they should choose for each type of hunting, some guidelines are provided below.

Stalking: 8×42 roof prism binoculars

Mountain hunting: 10×42, 10×50 roof prism binoculars

Raised hide hunting in the dusk, waiting in the dusk: 7×50, 8×56 Porro or Abbe–Koenig prism binoculars

*For glasses users, roof prism binoculars are a better choice because of the multi-stop eyepieces.

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