What is Binoculars? All Binoculars Features Explained


We’ve all seen and used binoculars, but few of us really go out and purchase one. This is partially due to the fact that we don’t have a precise purpose for the goods and only feel the need to have one when we go on vacation, especially to a picturesque location. However, many individuals, including sports fans, environment enthusiasts, and bird watchers, take their binoculars extremely seriously. When it comes to purchasing a device, these people are quite precise about the specs they want. What about the ordinary user, though? A guide on choosing binoculars may be found here.

The Basics

Binoculars Features Explained
Simply explained, binoculars magnify distant people, places, or objects by the use of a system of lenses, elements, and prisms. When you use two parallel optical tubes, you may view with both eyes open, which is more comfortable and natural than when you use a spotting scope or telescope, which forces you to close one eye. Furthermore, keeping both eyes open preserves depth of field and gives a rich and immersive experience in which the picture appears more alive and 3-D.

Between seemingly comparable pairs of binoculars, there might be a significant price difference. B&H, for example, has 10×42 binoculars ranging in price from around $30 to over $3,000. The quality of the optics, the types of coatings used to the lenses, and other characteristics that may be added, such as the housing material, are the major reasons for such a wide price range. Furthermore, the prism type may (and frequently is) a determining element in pricing. Because of the physics involved in developing and producing tiny roof prism binoculars, you can have a pair of the roof and Porro binoculars that appear to be equal in terms of quality and performance, but the roof prism version is frequently more expensive.

The good news is that if the form factor isn’t a problem, many people find that picking a Porro-prism improves the quality of their binocular without affecting their price.

The prism used in binoculars is technically a double-Porro prism, although it is typically reduced to just “Porro.” Because it is the last name of the creator, Ignazio Porro, who invented this prism system about 1850, it is usually capitalized. The folded light path defines this most basic of prism designs, which displaces the point where light enters and leaves the prism, giving it the look of a “traditional” or “old-school” binocular.

The name “roof prism” was first used in the Abbe-Koenig (AK) prism design, which rectified an image horizontally and vertically while preserving a straight line from the prism’s entrance to exit. While the AK prism is the most popular, there are others, such as the Amici and Schmidt-Pechan, that are variants of the original AK design (SP).

While they perform the same basic purpose, the optical pathways correct the picture alignment in various ways. The SP design has the benefit of being more compact than the Amici and AK prisms, resulting in smaller optical tubes that are more pleasant to hold—especially during extended glassing sessions. SP prisms are a trademark of Zeiss.

Porro prism binoculars are usually less expensive to manufacture than roof prism binoculars. Thus you can frequently buy a higher-quality and/or larger-objective Porro model for approximately the same price as a comparable roof prism model.

If you’ve been looking for binoculars, you’ve probably noticed that some are quite sleek, and others are chunkier. This is because the type of prism a binocular utilizes determines its physical look and size. Prisms are used to adjust the horizontal and vertical alignment of the vision so that the picture seems natural; without one, binoculars would make everything look upside down and flopped.

Prisms are divided into two categories: roof and Porro. Because the glass components of a roof prism are aligned, roof prism binoculars are more streamlined and simpler to grasp. When compared to similar roof prism types, porro prisms have the glass components offset from one another and can give a better depth of field and a broader range of view. Folding the light route shortens the length, allowing the targets to be spread out more.

Types Of Lenses

A lens is a bent piece of glass with a lentil-like shape. (If you’ve ever wondered where the name lens comes from, it comes from the Latin word for lentil.) Light rays slow down and bend as they strike a glass lens. A convex lens is one that bends like a lentil (like a dome), with the outside being thinner than the centre. 

Light rays are entering a convex lens bend inward toward the center as though the lens is pulling them in. A convex lens does this by bringing distant light rays into focus. Because it causes light rays to collide, it’s also known as a converging lens (converge). Convex lenses make objects look larger when seen through them, which is why they’re employed in magnifying glasses.

Another type of lens curves in the other direction, with the center of the lens being narrower than the edges. This is referred to as a concave lens. (If you imagine a concave lens cave in the center, this is easy to remember.) Light rays stretch out like fireworks lines when viewed through a concave lens. Consider how light rays enter a concave lens and then spread out in all directions. As a result, a concave lens is also known as a diverging lens. It causes light beams to erupt (diverge). In movie projectors, concave lenses are used to spread out the light from the film and cover a larger area as it strikes the wall.


The number printed with the x represents the magnification of a binocular. So, if the binocular reads 10x, that means the subject is magnified ten times. For example, a bird 1,000 meters away will appear to be 100 meters distant when viewed with the naked eye. The ideal magnifications for everyday usage are between 7x and 12x; anything higher than that will be difficult to operate without a trip scope.

Objective Lens Diameter

The objective lens is the lens on the other side of the eyepiece. The size of this lens is important since it controls how much light enters the binoculars. As a result, if you have a larger diameter objective lens, you will get better images in low light conditions. Following the x is the lens size in millimeters. In terms of magnification, a ratio of 5 is excellent. With its larger diameter, the 8×40 lens produces a brighter and better image than the 8×25 lens.

Lens Quality, Coating

The lens coating is crucial because it decreases light reflection while allowing the maximum amount of light to penetrate. Meanwhile, the lens’s quality guarantees that the image is free of aberrations and has superior contrast. Because they transmit more light, the best lenses perform better in low-light situations. They also guarantee that the colors aren’t distorted or faded away. If you use glasses, aim for a high eyepoint.

Field Of View/Exit Pupil

The diameter of the region seen through the glasses is measured in degrees and is referred to as FoW. The more field of view you have, the more area you can see. In the meanwhile, the picture created on the eyepiece for your pupil to view is known as the exit pupil. The exit pupil is calculated by multiplying the lens diameter by the magnification. A 7mm exit pupil provides maximum light to the dilated eye and is suitable for usage in the dark and dusk.

Weight & Eye Strain

Before purchasing a binocular, it is important to consider its weight. Consider whether using the binoculars for an extended period of time exhausts you. Similarly, try using a binocular to observe how tiring it is on your eyes. While conventional binoculars are difficult to use for more than a few minutes at a time, high-end binoculars do not cause eye strain and may be used for lengthy periods of time if necessary.


Because binoculars are mostly used outside, they must have some level of waterproofing, which is generally indicated by the letters “WP.” While normal models can only be submerged in water for a few minutes, high-end models are unaffected even after being submerged for several hours.

Eye Relief

The optimum distance between the eyepiece and your eye, or the focal point where light enters through the ocular lens, is called eye relief (eyepiece). Eyecups are installed on eyepieces by manufacturers to keep the user’s eyes at the appropriate distance from the eyepieces while using them. If you wear glasses, the eyepieces will be positioned past the eye relief distance, reducing visual quality and limiting your ability to attain fine focus.

Many binoculars have dioptric adjustments on one of the eyepieces, allowing most users to fine-tune the focusing mechanism to their eye prescriptions, allowing them to use the binocular without glasses. The eyecups are frequently movable if your prescription is difficult to read or if you’re using the binocular with other people.

Simple eyecups fold back to allow your eyeglass lenses to be placed closer to the ocular lens. Adjustable eyecups, for example, rotate in and out to precisely establish the correct distance for each unique user.

In general, glasses with longer eye relief have a narrower field of view than those with shorter eye relief that are equally priced. Optical engineering is a costly procedure for achieving outstanding standards in both areas. It’s usually beneficial to have a large viewing area, so figure out how much eye relief you’ll need and get the binoculars with the largest field of vision.

Coatings And Lens Materials

This is when sophisticated technologies (along with a bewildering number of words to describe them) enter the picture. The quality and brightness of your vision are determined by the composition of the glass and the anti-reflection coatings on the lenses. This is when test watching comes in handy. This will inform you how far your eyes can notice improvements and, as a result, how much more you should contemplate paying for the visual quality you desire.

Prism Type

The optical components that guide light from the picture through the binoculars to your eyes are known as prisms. The front barrels of older “porro prism” binoculars are broad and not aligned with the eyepieces. Eyepieces and objective lenses are aligned in newer “roof prism” versions. Although the change in appearance has no bearing on optical quality, roof prisms allow binoculars to be smaller and lighter.

Rubber Coating

While a rubber covering will not give full-scale crash protection, it will aid to protect against small bumps and bruises. It’s a useful feature for any binoculars that will be utilized in harsh outdoor conditions.

Fog-Proof Binoculars

When you shift from a cold to a warm location, binoculars might fog up. Not only is this inconvenient, but it can also be hazardous if moisture becomes trapped within.

Binocular manufacturers purge the air within the binoculars and replace it with nitrogen, which has no moisture content and so does not condense. This just protects the interior lens surfaces from fogging, not the external ones.

Lens Coatings

Lens coatings are thin films that are placed to the surface of lenses to minimize glare and reflections, improve light transmission and contrast, and make colors appear more vibrant. Because any light reflected never reaches the viewer’s eyes, removing reflections makes the image brighter and clearer.

Coatings are fine in general, as long as they accomplish anything. Although it’s simple to apply an inexpensive coating to a lens to give it a cool-looking orange hue, the coating may not enhance image quality. If you can’t try a pair of binoculars before purchasing, the best you can do is study the brand, read user reviews, and ask questions.

Coated, multi-coated, and completely multi-coated are terms that relate to the location and type of coating procedures that are employed. Coated lenses are the most basic, and they have at least one layer of coating on at least one lens surface. Multi-coated refers to the coating of numerous surfaces and/or the application of multiple layers of coatings to each surface.

Fully multi-coated lenses have several layers applied to both their inner and exterior surfaces. The maximum amount of light transmission, clarity, contrast, and color rendition is achieved with this treatment. Broadband completely multi-coated is at the pinnacle. These coatings are designed to work across a wide range of wavelengths and deliver the greatest results.

Prism Coatings

Prism coatings, which increase light reflection and improve picture brightness and contrast, are a good complement to lens coatings. While many manufacturers employ conventional reflecting coatings, dielectric coatings enable nearly 100% of the light to pass through the prism, resulting in brighter, higher-contrast pictures.

The “phase-correcting” coating is a form of prism coating that is exclusively used on roof prisms. Because of the way roof prims reflect light, it splits into two distinct beams that go through the prism system separately after passing through the objective lens. When one beam strikes the eyepiece lens a fraction of a second before the other, there is a “phase shift.” The two beams are slightly out of phase when they are recombined in the eyepiece lens, which might alter color balance and rendition.

The quicker light beam is delayed to match the slower light beam by adding specific coatings to the prism, putting them back into phase as they strike the eyepiece lens—significantly enhancing color, clarity, and contrast over non-phase-corrected prism binoculars. Most users won’t notice the change under normal conditions, but pro users and ardent birdwatchers may require it to be able to pick out critical features at a distance or in dim light. These coatings are not utilized on Porro prisms since they do not suffer from phase shifts.


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