Getting Started

Pricing

• How much should I pay for a pair of binoculars?

Understanding the Numbers

• What does the first number in a binocular mean, i.e., the 8 in 8 x 40?
• What does the second number in a binocular mean, i.e., the 40 in 8 x 40?
• What is Field of View?
• What determines Field of View in a binocular?
• What is Exit Pupil?
• What is Relative Brightness (RE)?
• What is twilight factor?
• Why are there so many low-light measurements?
• What is interpupillary distance?
• What is "minimum focus" or "close focus"?
• What is eye relief?
• How much eye relief is needed when wearing eyeglasses?
• Should the eye cups be up or down?

Prism Designs

• What is a prism?
• What is a porro prism?
• What is a roof prism?

Lens Coatings

• What are lens coatings?
• What are the different types of lens coatings?
• What is "fully coated"?
• What is "multi-coated"?
• What is "fully multi-coated"?
• What is Bak4 or BK7?

Focusing

• What is a center focus binocular?
• What is an individual eyepiece binocular (IF)?
• What is a "no focus" or "focus free" binocular?
• What is the diopter adjustment on a binocular?
• Where is the diopter adjustment located?

Weighing In

• How much weight in a binocular can I carry around my neck?

Exterior Features

• What is a waterproof binocular?
• Do I need waterproof binoculars?
• What is an armored binocular?

Accessories

• Can I mount any binocular to a tripod?
• Where is the tripod adapter located?
• Do I need a tripod?

Binoculars are the second most frequently used optical instrument in the world, with eye glasses being number one. However, buying eyeglasses is relatively easy when compared to buying binoculars. When buying glasses your opthamologist provides you a lens (magnification) prescription at the conclusion of an examination, and all you have to do is select a frame that you like and are willing to pay for. On the other hand, buying the right pair of binoculars requires a good grasp of the various terms, features, and specifications associated with binoculars; understanding how they inter-relate with one another, and then prioritizing the importance of each so that the binocular selected is the right fit for the activity or activities it is being purchased for. First-time buyers of binoculars are often surprised to learn that power (magnification) is not the only factor to consider, and it is rarely most important. If you were to start mixing and matching all the many attributes and features of binoculars that are offered across all binoculars, the number of binocular choices you would have would be unmanageable. From both an application and performance perspective, each would yield entirely different results, with none being exactly the same from one binocular to the next.

This is not to suggest that purchasing a pair should seem like quantum physics, or even buying a car for that matter. We just want to help you make the selection process easy, given how uneasy the introduction of new terminology can make people feel. We also want you to be educated prior to purchasing. After going through this guide we are confident that you WILL become adequately educated, and will find that making a binocular purchase really is EASY after all.

This guide provides straight forward definitions and answers to most of the common questions first time buyers have. As you read through it, always keep in mind that a good pair of binoculars simply offers a bright, clear view that will not cause eye strain and a weight that will be comfortable for carrying given your activity of preference. For first timers especially, the difficulty will be in determining which factors are most important to you, since choosing quality in one often means diminished quality in the others-or a higher price. And lastly, and perhaps most importantly, once you understand these features, you will then have to simultaneously factor in the primary activity or activities you will be using your binoculars for. Although binoculars are versatile optical instruments, each binocular is certainly not best suited for; nor can each binocular be applied to every activity, hobby, and sport that exists.

Pricing

Q1. How much should I pay for a pair of binoculars?

A1. Prices for binoculars range from $30 to over $1,000, so you should first determine how much you can afford before considering all the options. There are many birders and hunters who are of the opinion that no binocular that costs less than $400 is worth owning. Please remember that these are opinions only; and that while these persons are certainly not wrong, they may share interests, experiences, and enthusiasm levels that differ from those of your own, each of which weigh heavily into the formulations of such opinions. Believe me, you can find a pair of inexpensive binoculars that you will be completely satisfied with, and you can also find an expensive pair of binoculars that doesn't ultimately suit your needs. Be comfortable with the amount you want to spend, and once you decide, you will likely eliminate many brands and models from consideration. Then begin looking at the binoculars with the highest-quality optics--glass, prisms, and coatings that are available in your price range. From here, you will apply them to your interests and activities; along with the features that are most important to you: magnification, aperture, design, construction, weight, etc.

Understanding the Numbers

Knowing what the numbers mean is the first requirement. From here you will begin to understand the how various binocular features and attributes interrelate with one another, and will ultimately help you to evaluate and compare performance levels of binoculars you are interested in purchasing.

Q2. What does the first number in a binocular mean, such as the 8 in 8x40?

A2. The first number - the ‘8' in an 8 x 40 or ‘10' in a 10 x 42 is the magnification. Magnification simply means how many times the image is enlarged over its normal size when you look through the binocular. Stated another way, magnification is how many times closer the subject appears to be in a binocular than it actually is. When looking at an object 100 yards away through a 10 x 40mm binocular, the subject will appear to be ten yards away.  Always remember that a 10x50, 10x40, and 10 x 42 are all 10x binoculars and each magnify an identical 10x.

Note that in ‘zoom binoculars', the first two numbers out of three, represent the magnification range. In a 7-15x40, for instance, you can change the magnification from 7x up to 15x by ‘zooming' in.

Be careful with magnification because more is not always better.  The affect of higher magnification means that both the image brightness and field of view (the amount of territory seen through the binocular) will lessen. And also equally as important, image steadiness also decreases. A binocular not only magnifies the image you are viewing, it also magnifies even the slightest shake of your hand when holding it, which obviously impacts the binoculars' performance. Most people, and particularly birders, find that a 10 x binocular is the highest magnification that can be comfortably steadied without the support of a tripod. Hence the introduction of the terms, ‘hand held' and ‘tripod adaptable' that are often associated with binoculars.

Q3. What does the second number in an 8 x 40 binocular mean?

A3. The second number in a binocular - the 40 in 8 x 40mm or 50 in a 10 x 50mm - is the diameter (width) of each front lens (commonly referred to as the ‘objective lens' or ‘objective diameter'), measured in millimeters.  This number is also referred to as Aperture, and is derived from the Latin word aperire ("to open"). The objective lens size, or Aperture, is the determining factor for the amount of light captured in an image and has a direct impact on binocular performance. When magnification and quality is equal, larger objective lenses will produce brighter and sharper images. An 8x40, then, will produce a brighter and sharper image than an 8x30, even though both magnify the image an identical eight times. The larger objective lenses in the 8 x 40 also produce wider beams of light (exit pupil) that leave the eyepieces. This makes viewing more comfortable with an 8x40 when compared to the 8 x 30.  By allowing more light to be captured in an image, the larger objective lenses are ideal for low-light conditions, i.e, viewing right before dusk; viewing in wooded areas with a significant amount of tree cover; and viewing under cloudy skies. Most recreational binoculars range from 20mm to 60mm.  As in the case of magnification, bigger isn't always better. In order for the lenses to allow more light in, they have to be bigger. And bigger means heavier. The larger objective lenses in the 8 x 40 binocular make the 8x40 bigger and heavier than the 8x30 binocular.  An 8x30 may not optically out-perform an 8x40, but its smaller size and weight make it a better traveling companion. The difference in weight here may translate into only 10 or 15 extra ounces and may not seem significant to you now. But two and three day hiking or birding excursions with this extra weight may cause neck strain (if using a neck strap) and increase physical and mental fatigue. Lifting binoculars to eye-level a couple of hundred times over several days will be also be easier if you are lifting less weight, no matter how strong you are. Please keep in mind that a lighter compact binocular will outperform any full size binocular left at home or in the car because it was too heavy to carry.

Q4. What is Field of View?

A4. The field of view is the width of the area that can be seen through the lens, and is commonly described as FOV. This measurement is expressed in terms of linear feet viewed from 1,000 yards or in ‘degrees of field', with 1 degree of field equal to a linear view of 52.5 feet.  To illustrate, suppose you are 1000 yards away from a fence and viewing it using a binocular with a field of view of 372 feet at 1000 yards. You will see 372 feet of the fence.  This same binocular has a ‘degrees of field' measurement of 7.08 (372 divided by 52.5). Most binoculars have FOV's that range from 250 to 600 feet, or roughly 5 to 11 degrees. When manufacturers talk about "flat field," they're referring to a sharp, clear image across the entire field of view.
 

Q5. What determines the field of view in a binocular?

A5. Field of view is determined by magnification and the eye piece design.  In general, as magnification increases, FOV decreases.  A 10x will show more detail in that fence at 1000 yards than an 8x, but it will not show you as wide a section of fence. Binoculars employing a wide-angle design eye piece will enable you to see a wider section of the fence than binoculars a standard eye pieces. High quality Wide-Angle design pieces are usually very expensive; while inexpensive binoculars with wide angle eyepieces do not usually yield the same crisp images that standard binoculars do. Although a wider FOV is preferred when viewing fast moving action like flying birds or horse racing, please note that a FOV difference of 30 feet at 1000 yards is not significant.

Q6. What is Exit Pupil?

A6. The exit pupil in a binocular is the actual width of the beam of light that leaves the eyepieces and is measured in millimeters. You can see the exit pupil by holding the binocular up to eye level at arm's length. The circle of light in each eyepiece is the exit pupil. To calculate the size of the exit pupil, divide the magnification power into the objective diameter size. A 10x50, 7x35, and 8x40 each have an exit pupil of 5. Higher magnifications generally lead to lower exit pupil.

Q7. What does exit pupil tell me about a binocular?

A7. Exit pupil is a general guide to determining image brightness. Binoculars with large exit pupils provide brighter images under very low light conditions. For normal daylight viewing, an exit pupil of 2.5 or 3 is adequate. For astronomy or when viewing at sunset, an exit pupil of 5-7mm is preferred. An exit pupil larger than 7 does not use light efficiently because the human eye cannot open wide enough to accept exit pupils larger than this. For repeated low-light viewing we recommend a minimum exit pupil of 4.

In addition to providing more light at dusk or when light conditions are less than ideal, a large exit pupil does provide other advantages. A large exit pupil is easier to keep centered on your eye when it is difficult to hold a binocular steady, as in the case of being on board a moving boat.  This is the reason that traditionally, Marine binoculars are 7 x 50mm. 

Q8. What is Relative Brightness (RE)?

A8. Relative brightness is commonly referred to as ‘RE', and like exit pupil, is a rough guide to image brightness. It is simply exit pupil squared, so a binocular with an exit pupil of 5mm will have an RE of 25.

Q9. What is twilight factor?

A9. This is a mathematical formula that estimates the amount of detail that can be seen in low light. Twilight factor is the square root of magnification multiplied by objective diameter. A 10x40 will have a twilight factor of 20 (square root of 10x40).

Q10. Why are there so there so measurements for measuring performance in low-lighting?

A10. We are not sure why there are three different measurements that lead to virtually the same conclusion around a binoculars' low-light performance. We do know that each term, Exit Pupil, Relative Brightness, and Twilight Factor; is included in the ‘specifications' section of the product descriptions provided by most major binocular manufacturers. We just want you to understand them prior to making a purchasing decision.

Also, it is very important to note that these measurements (Exit Pupil, Relative Brightness, and Twilight Factor) are to be used as a rough guide only, and are not to be taken too literally. Each of these measurements treats all binoculars, regardless of lens coatings and optical quality, as if they are the same. A $70 binocular will never be equal to a premium grade binocular for low light detail, even if they both have the same exit pupil, relative brightness, and twilight factor.  Actual test results have concluded that some premium-grade compacts with low relative brightness are actually brighter than some lower grade full-size binoculars.

Q11. What is the interpupillary distance (IP)?

A11. The interpupillary distance is the distance between the pupils of the eyes. All binoculars can be opened wider or closed tighter to accommodate different widths. Occasionally people with very small faces or people with very large faces have a more difficult time finding a binocular that will fit them correctly.

Q12. What is the "minimum focus" or "close focus"?

A12. The "minimum focus" or "close focus" is the nearest distance at which a binocular will focus on an object. A binocular will not focus on an object closer than this distance. This feature is important for birders to consider. Most birders require a close focus of 13 feet or less.

Q13. What is eye relief?

A13. Eye relief is the maximum distance your eye can be from the eyepiece and still see the entire field of view. If your eye is farther back than this distance, you will see a reduced field of view. Eye relief is of primary concern for people who wear eyeglasses when they look through a binocular because their glasses prevent their eyes from getting close to the eyepieces.

Q14. How much eye relief is needed if you wear eyeglasses when looking through a binocular?

A14. If you have fairly thin plastic lenses in your eyeglasses and a small face, 13mm will probably be enough. The minimum eye relief required for most eye glass wearers is generally 14 or 15mm. If you have eyeglasses with thick glass lenses, you should look for a model with eye relief in the 17-20mm range.

Q15. Should the eyecups on a binocular be in the "up" position or "down" position when using eyeglasses with a binocular?

A15. The eyecups should be in the "down" position when wearing eyeglasses and in the "up" position when not wearing eyeglasses. Older style binoculars have rubber fold down eyecups, but most binoculars manufactured in the last few years have "twist up" or "pull up" style eyecups.

Prism Designs

Q16. What is a prism?

A16. A prism is a glass element used to produce an upright, correct right to left image in a binocular. Without a prism, a binocular would produce an upside down image. Binoculars manufactured today use two types of prisms: a porro prism and a roof prism.

Q17. What is a porro prism?

A17. A porro prism is an image erecting system that was designed and patented by the Italian optician, Ignazio Porro in the 1850's. Today, porro prism binoculars use a porro prism in a double prism Z-shaped configuration to erect the image, resulting in binoculars that are wide, with objective lenses that are well separated and offset from the eye pieces.   In other words, the eye piece and the objective lens in a porro prism are never in a straight line. A porro prism is a larger and bulkier prism than a roof prism; and because of this, the body of a porro prism binocular will also tend to be bulkier.  Porro prism binoculars inherently produce brighter images than roof prism binoculars of the same magnification, objective diameter and optical quality; and are less expensive to make than a roof prism. This makes a quality porro prism binocular every bit as good optically as a quality roof prism and at a much lower cost. If your priority is getting the most optics for your dollar, especially in a binocular under $200, we recommend a porro prism.

Q18. What is a roof prism?

A18. A roof prism is a smaller prism that is shaped like a house with a roof. You can always recognize a roof prism by its shape. Unlike porro prisms, the objective lenses are approximately in line with the eye pieces. The main advantage of a roof prism is its size and shape. It is smaller and more compact than a porro prism and can be installed in a sleeker housing than a porro prism. This makes a roof prism binocular a nicer binocular to hold and handle for most people. 

Conversely, a roof prism is much more expensive to make to the same optical standards as a good porro prism because they employ silver coated mirrors that reduce light transmission by as much as 15%. Porro prisms do not use mirrors and do not have the light loss factor to contend with that roof prisms have to as a result. Roof prisms also require tighter tolerances for alignment of their optical elements (collimation), further adding to their expense because the design requires them to use fixed elements that need to be set at a high degree of collimation at the factory.

This need for precise alignment in a roof prism does have benefits, however.  A roof prism is solidly housed in a cage and the focusing mechanism is usually inside the binocular instead of outside as in many porro prism binoculars, making a good roof prism binocular more rugged and smoother focusing than the average porro prism binocular. It is also less likely that that roof prisms will ever have to be brought back to the factory for re-alignment, whereas porro-prism will occasionally require their prism sets to be re-collimated.

Lens Coatings

Q19. What are lens coatings?

A19. Lens coatings are chemical coatings on the lenses in a binocular that make images brighter. Binoculars can have up to 16 air-to-glass surfaces. When light strikes each surface, some of the light is transmitted, and some of the light will be reflected. In an image forming optical instrument such as a binocular, ideally no light should be reflected. Instead of forming an image, light which reaches the viewer after reflection is distributed in the field of view, reducing the contrast between the true image and the background. Reflection can be reduced, but not eliminated. A binocular without coated lenses could lose as much as half of its incoming light.

Q20. What are the different types of lens coatings used in a binocular?

A20. There are three categories of lens coatings used in a binocular: fully coated, multi-coated and fully multi-coated.

Q21. What is a "fully coated binocular"?

A21. A "fully coated" binocular are the oldest and least efficient type of lens coating - a single layer of magnesium fluoride. This type of lens coating is found only on inexpensive binoculars and will not produce images as bright as multi-coated binoculars.

Q22 What is a "multi-coated binocular"?

A22. The best lens coating in binoculars consists of complex multiple-layers of chemicals. This type of coating is called multi-coating and it allows the maximum amount of light to pass through the lens. A binocular labeled as "multi-coated" will have some, but not all lenses multi-coated and will yield brighter images than a "fully coated" binocular.

Q23. What is a fully multi-coated binocular?

A23. A binocular labeled as "fully multi-coated" or FMC will have all of its lenses multi-coated and yield the brightest image of any coating system. All quality binoculars will be "fully multi-coated".

Q24. What is Bak4 or BK7?

A24. These are grades of optical glass used in the prisms of binoculars. The highest quality prisms are made with high-density BAK-4 glass, giving optimal clarity and brightness. Only inexpensive binoculars use the inferior BK7 grade of glass.  

Focusing

Q25. What is a center focus binocular?

A.25 A center focus (CF) binocular uses a centrally mounted wheel or lever that adjusts both eyepieces simultaneously. CF binoculars are the most versatile and commonly used focusing system in a binocular. Most CF binoculars come with a focusing device on one of the eye tubes (diopter adjustment) that will compensate for differences in the strength of each eye.

Q26. What is an individual eyepiece focus binocular (IF)?

A26. An individual eyepiece focus binocular requires you to focus each eyepiece individually when viewing an object, but once the focus is locked- in, objects from 40 yards away to infinity are always in focus and require no additional focusing. This is a great system for viewing objects at medium and long range distances, but it is obviously not suited for viewing objects at close range in work. IFs are most commonly found in marine binoculars and astronomy binoculars.

Q27. What is a "no focus" or "focus free" binocular?

A27. This is an inexpensive version of an individual eyepiece focus binocular, but the eyepieces are locked and set at the factory and cannot be adjusted. This means that you can never focus on objects closer than forty yards away and it also means that the binocular cannot be adjusted for differences in strength between your right eye and left eye. This is a serious shortcoming for most people, since most have do not have eyes that are of equal strength.

Q28. What is the diopter adjustment on a binocular?

A28. The diopter adjustment on a binocular allows you to compensate for differences in strength between your right and left eye. Since most people have one eye stronger than the other, this is a feature found on all binoculars except for "focus free" models.

Q29. Where is the diopter adjustment on a binocular located?

A29. The diopter adjustment has been traditionally located on the right eyepiece, but many models today use a separate wheel or a locking mechanism on the center focus knob.

Weighing In

Q30. How much weight in a binocular can I carry around my neck?

A30. Binoculars can weigh anywhere from less than 1/2 pound to 5 pounds or more. The debate around weight is always portability versus performance with all other things being equal. Objective diameter size is the main factor in determining weight. Binoculars with and binoculars with a large field of view tend to have bulky designs. Prism style and construction can also affect heaviness. As mentioned in the discussion about objective diameter sizes, you should consider your activity carefully. The importance of the weight factor depends on your prime uses. Most backpackers will want a small, lightweight pair of binoculars that can easily fit into a pack or pocket. Bird watchers who generally take only day hikes can afford a heavier, bulkier pair--1-1/2 to 2 pounds. Portability isn't as much of a consideration for backyard birders or sport spectators who simply want a close-up view of the action.

Most people find that anything more than 35 ounces is too much to comfortably carry around the neck and a weight of less than 30 ounces is much better. Carrying full-size binoculars for  extended-use activities like hiking, birding, and hunting will can use mental and physical fatigue more quickly. We recommend a binocular harness, as opposed to a neck strap, when carrying a full size binocular over lengths of time. The binocular harness supports the weight on your shoulders rather than on your neck and will be a difference maker.

Exterior Features

Q31. What is a waterproof binocular?

A31. A waterproof binocular is one that is guaranteed by the manufacturer not to fog up as a result from moisture entering the inside of the binocular. All binoculars will fog up on the outside. You will see the terms ‘water proof' and ‘fog proof' linked together often. They are one in the same. A binocular is made waterproof and fog proof by filling (purging) the binocular with nitrogen. Please do not confuse such terms as ‘water-resistant', ‘rain-proof', and ‘rain-sealed' with water-proof. These terms do NOT guarantee a binocular to be waterproof.

Q32. Do I need a waterproof binocular?

A32. If you are using a binocular around water or during rainy conditions, waterproofing is a necessary feature. Even for more casual use, though, a waterproof binocular is a better sealed binocular and less likely to develop problems with dirt and dust entering the binocular. We recommend that you purchase a water proof binocular no matter what activity you are purchasing them for.  Weather is not predictable enough and this feature will go a long way towards preserving your binoculars' integrity.

Q33. What is an armored binocular?

A33. An armored binocular is a binocular with a housing covered by rubber or other synthetic material. Please note that Armoring does not make a binocular water proof, but it does protect it from scratches, makes it more comfortable to hold and also reduces the impact made when a binocular is dropped.

Accessories

Q34. Can I mount any binocular to a tripod?

A34. You can only mount a binocular to a tripod if it is ‘tripod adaptable' or if it is threaded for a tripod adapter. If it is listed as tripod adaptable, you will still need to purchase a tripod adapter, though there are full size binoculars that have this accessory built in. Most tripods and adapters are manufactured to fit all binocular brands and models. However, there are other tripods that are made exclusively to be attached to only their own binocular lines. Be sure you make the appropriate inquiries prior to buying your tripod.

Q35. Where is the tripod socket located on a tripod adaptable binocular?

A35. It is usually located at the front of the center hinge where the binoculars fold and is often hidden under a cap.

Q36. When do I really need a tripod?

A36. We recommend that any time you have a binocular magnification that is greater than 10x you attach the binocular to tripod to steady the image.  Additionally, binoculars with objective diameters (objective lens) that are greater than 60 are usually heavy and easier to use while atop a tripod that supports the weight. Birders requiring high magnification to view their subjects often switch over to a spotting scope, rather than trying to steady binoculars with their hands. Spotting scopes generally have more power than binoculars and are often offered with tripods included.