The Basics of Binoculars

The first thing to know is that they are one of the most popular optical instruments used in the world that is, of course, after the use of eyeglasses. They come in a wide variety of styles, sizes, uses and prices. Knowing what you will use them for is the first step into choosing the right instrument for you. Lets start with understanding the fundamentals; what are binoculars and what are they used for?

They are an optical instrument that allows the user to view objects in the distance clearly. They consist of two small telescopes situated side-by-side, each having a pair of lenses that will bring the objects closer and a pair of prisms in each side to bring the image right-side-up. The telescopes are positioned in the same direction, enabling the user to view the object with both eyes. The image to the left shows how the instrument effectively works in order to view the object.

When shopping for a pair, you will see that the main specifications are presented by two numbers with an “x” in between such as 7x50. The first number you see, including the x represents the magnification or power, in this case being 7x. This signifies the degree in which the object is enlarged. In this situation the object appears to be 7 times closer to you then when looked at with the naked eye. Of course, different models offer different magnifications, but they normally range from 5x to 8x. If the magnification exceeds 10x, they will be heavy and most likely you won’t be able to hold them steady enough to get a fixed picture. For anything over 10x it is recommended to use a tripod-mount to stabilize the image and get optimal vision. The second number that is presented in the formula is the aperture. This means that it presents the diameter of the objective lens or the front lens, which are the lenses further from your eyes. In the example 7x50, the instrument has 50 millimeter in diameter objective lens. Why this would matter to you is because the aperture determines the ability your instrument has to gather light. The larger the objective lens the brighter the image. This makes a difference when you are viewing something in low light conditions in comparison to bright sunny days. Another specification you will find along with the magnification and objective lens is the exit pupil. It is the size of the circle of light visible at the eyepiece. The exit pupil is signifies how bright objects will appear in low light conditions. It can be calculated by diving the object lens diameter by the magnification, and the higher the number the brighter the image. Therefore, in our example 7x50, the exit pupil would be 50 divided by 7, which would be a little over 7 millimeters in diameter. Note that for daylight viewing an exit pupil of 2.5 or 3 would suffice. As for nighttime viewing such as astronomy, an exit pupil of 5 to 7 mm is suggested. Anything over 7 mm is not needed as the human eye cannot open wide enough to accept this amount of light.

Relative Brightness

Much like the exit pupil the relative brightness is a determinant of the image brightness. The relative brightness is calculated by squaring the exit pupil number. For example if the exit pupil number is 5, square 5 (5x5) you get the relative brightness number of 25. This shouldn’t be taken too literarily because it doesn’t weigh in other factors the instrument has.

Twilight Factor

This calculates the mount of detail that one can see in a low light situation. The formula is the square root of the magnification multiplied by the objective lens. In our example 7x50, if we multiple 7x50 we would get 350 and the square root of 350 is 18.7. Therefore, the twilight factor is 18.7. Again, much like the relative brightness and the exit pupil, this number should not be taken too literarily because it does not factor in other features the instrument has.

Eye Relief

This refers to the distance between your eyes and the binoculars while the whole field of view is still visible. Longer focal length of an eyepiece, gives greater eye relief. This is ideal for people who wear eyeglasses and manufacturers have made instruments with twist-up, pop-up or soft rubber fold-down eyecups, which go down. It is recommend that eyeglass wearers look for an eye relief of 11mm or more. For those who have different vision in each eye, there is a diopter adjustment that will give the viewer a better experience. It is a ring situated behind the eyepiece lens that allows you to focus each lens individually. Also, there is an inter-pupillary distance number, which refers to the distance between the eyes of a person. This obviously differs from person to person and can be fixed by opening or closing the hinge to either bring the eyepieces closer together or further apart. Typically the inter-pupillary distance ranges from 60mm to 72mm.

Field of View

Is the measurement of area that can be seen through your optic. It is the width of the area, usually in feet, visible at 1000 yards or meters. The field of view can be measured by two things; the magnification and the eyepiece design. First thing to know is, when the magnification power is higher the field of view is lower. Therefore, when looking at an object at 1000 yards a 10x will show you more details of the object than an 8x, but you will not see it in a wide view. The wide-angle design also is a determinant of the field of view. This matters if using the instrument for astronomy, a wide field of view will be more desirable to see the sky at a fuller view, making the experience more enjoyable. Most of the instruments have focus knobs and what this will give you is the “close focus”. This being the closest distance your instrument will focus on an object. This feature is one to look out for if you are using your instrument for bird watching.

Types of Binoculars

They come in different shapes and the type of prism they use determines the style or shape. There are two different prism systems; the Porro and the Roof prism. There are advantages and disadvantages to each kind and the instrument for you comes down to your specific need and preference.

Porro Prism

The Porro prism binoculars are easy to distinguish as the objective lens is offset of the eyepiece. The advantage to this specific instrument is that it gives the viewer a greater depth perception and a wider field of view. A quality pair would relatively be cheaper than a roof prism. It is less compact but is great for any general use or activities such as bird watching and other sporting events.

Roof Prism

The second of the two main systems is the Roof prism. In this system the prisms are overlapping each other in a straight line giving a sleeker streamlined shape. This instrument is compact, making it easier to take around.

Standard Size Binoculars

Standard Size Binoculars – “full-size” common specifications being 8x42, 10x50. They capture more light and therefore perform better in low light situations. This choice may be heavy for backpacking, but perfect for mariners or wildlife enthusiast.

Compact Size Binoculars

Compact – they are smaller and more portable due to their lighter weight. Recommended for activities such as hiking, theater, or long hunting trips

Wide Angle Binoculars

Wide Angle – because they give a wider view they would be most suitable for watching a fast moving object, such as watching a game in a field, racetracks or wilderness excursions

Zoom Binoculars

Zoom – from its name it allows the viewer to increase the magnification enabling them to focus on a distant object in a closer more detailed view

Waterproof Binoculars

Waterproof - perfect for someone who will be spending time at sea; it gives them clarity in the harshest of conditions

Objective Lenses

As you now know, the main job of the objective lens is capturing as much light as it can and deliver it to the eyepiece. In order to achieve a more substantial amount of light transmission, the optics are coated with special chemicals. Damaged objective lenses whether it’s a scratch or a chip; will render the optic useless. This makes the objective lenses the most important element of the instrument and needing to coat it would be the most expensive part of the binocular. There are different amount of layers a lens can be coated with. A Coated lens would indicate that there is a single layer on one lens surface. A Fully Coated lens signifies that there is a single layer on all air-to-glass surfaces. A Multi-Coated layer implies that there are multiple layers on at least one of the lens surfaces. Lastly, the Fully Multi-Coated lens indicates that there are multiple layers on all air-to-glass surfaces, giving it the possibility to achieve 95% light transmission. What this means is that 95% of the light absorbed by the objective lens will reach the eye. The more coating there is on an objective lens the better resolution you receive getting the image appear more clearly opposed to a less coated lens.

Uses of the Binocular

The uses for them vary from outdoor activities, bird watching, hunting, sporting events, astronomy or even theater watching. Knowing what you will be using them for will help you buy the right pair for you. Lets take a closer look at the uses it offers.

Binoculars for Outdoor Activities

The best option for daytime outdoor activities would be the compact, wide-angle binoculars. You can get right in the action when watching sporting events at a stadium, going hiking or wanting to see in the distance while out for a bike ride. The wide- angle gives you a clear view of the entire stadium and the specs usually range from 7x to 10x, the common being 8 x 25 or 10 x 25. They are the lightest and smallest of the options, which is great when backpacking or wanting one to be around your neck for an extended period of time.

Bird Watching

Bird watching is becoming an increasingly popular hobby amongst many people. The most sought after for optic for bird watching is an 8 x 42, giving you the capability to see the detail of the bird. You may ask why not get a 10x or more? Higher magnifications have disadvantages for bird watching:

• Heavier to hold
• Smaller field of view
• It will offer you a slightly more detailed view, but will essential not make that big of a difference, so you will be paying more, for not much more.
• Less light, so bird image won’t be as bright
• More difficult to see closer objects
• More hand strain because you will have to hold it more steadily to get proper image

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Consider a longer eye relief and a close focus when choosing your bird watching instrument!

Hunting

Hunters who have spent time searching for elk, anticipating on a moose or even stood in a deer stand recognize the importance of using binoculars for a successful hunt. This instrument will guide your vision to animals and scenery easily missed while adding to the enjoyment of such outdoor activities. They are a necessity for those with an interest for hunting and adventure. The process of choosing the right pair is all about the lighting. Hunters rely greatly on the time of day, whether its dawn or dusk. Therefore, the most preferable choice of binoculars consists of: 7x to 10x magnification, low light performance, full sized 42-50mm, and objective lenses.

Astronomy

When most of us think about looking at the stars and constellations, we think we need the big telescopes we often see in the movies. Little do we know that there are specially designed binoculars that enable stargazing. They consist of enormous magnifications and objective lenses that absorb as much light as possible; making it possible to watch the stars. They are usually known as ‘Giant Binoculars’ and they range from 10x50 to 25x100. The higher you choose, the heavier it will be and most likely you will need a tripod, especially since your hands shaking is amplified by larger magnification.

Marine

For this purpose typically any binocular could be used for mariners and boating enthusiasts. Naturally there will be more fitting options for the sea, such as being waterproof or have a rubber armoring. You should choose one with an optimal magnification, adequate light grasp and good image quality. It is common to use a magnification of 7x with a 42 or 50-millimeter objective lens.

Concert/Theater/Opera

We’ve all seen movies that have an opera attendee holding a small binocular in their hand watching the show through the spectacles. These are perfect for those who are watching a concert, theater or opera and need that extra boost in vision to properly view the details of the set and the amicable costumes without putting additional pressure on their eyes. The compacts with a wide angle are ideal for any concert, theater or opera goer. While considering the style and design of the instrument, knowing the proper magnification and focusing abilities will make your show a more enjoyable one. The 4x30, 5x25, 8x25, 7x18 or 7x21 would be your best choices.

Tips

Weight – as a general opinion, most people find that a comfortably fitting instrument would weigh 30 ounces or less. It makes carrying it around your neck easier and less of a pain. If you do have one that weighs over 30 ounces you make want to consider getting a harness that supports the weight on your shoulders rather than all the weight being on your neck.

Tripod Mounting – you will need to have one ready for use when your instrument has a magnification over 10x or 12x. As we have said before, the larger the magnification the heavier the instrument and the more susceptible you are to shaky hands and shaky image. Many large optics come with a tripod adaptable, but if yours does not it can easily be purchased as an accessory.

Cleaning the Lenses – use a microfiber cloth, which usually comes with the instrument, and in a circular motion wipe the lens. This will protect the coatings on the lenses. Be aware of sharp objects when you clean or use the objective lens, they are sensitive and if damage comes to them the instrument will deem to be useless.

Now that you have a basic understanding of how they work, features, what they can be used for, with the activity they will be used for and the budget in mind your decision in choice will be an easy one. Remember to try it for a feel, is it too heavy are the eyepieces too close together, do you need a tripod? Look around and carefully take your pick, as you may be picking your lifetime binocular!