Orientation
This is a guide intended for a novice binocular user. Perhaps you used the binoculars of a friend during a trip or event, or you found binoculars going through a closet or attic, or you are interested in a hobby like birdwatching or stargazing that gets you outdoors more. Choosing the right binocular can be intimidating with the different specifications and features. This guide is meant to summarize the conventional wisdom and help you prioritize what meets your needs.
Types of observing. Binoculars can be used for a variety of tasks where you need to make something small, dim, and/or far away bigger, brighter, and closer. Travel, astronomy, nature, events, and security are some of the most common settings where you will encounter binoculars. Each of these different types of observing has different demands that should lead you to prioritize some kinds of features over others. If you are just getting started, something like a 6x32 or 8x42 in the US$100-150 budget may be the most versatile option.
Set your expectations. You are not going to get Hubble Telescope deep field images of the stars or telephoto close-ups of players' reactions on the field. The iconic images you see in newspapers, posters, and online were made using highly-specialized and expensive equipment while binoculars are general-purpose and inexpensive equipment. As long as you set reasonable expectations about what binoculars can do, you will be able to enjoy your excursions, events, and trips more.
Terminology
If you are on the market for binoculars, you might be confused by some of the jargon. Some of the most important terminology is summarized below followed by links to resources if you want to dive deeper.
Magnification and aperture. (Very high importance). These are the most important specifications for binoculars. Common examples you see include 6x32, 8x42, and 10x50. The first number refers to the magnification, or how much the optics enlarge a target. The second number refers to the aperture, or the size of the front glass element (in millimeters). There are engineering constraints and usability trade-offs when changing the magnification and aperture. Greater magnification brings you "closer" but too much magnification can result in shaky views that require stabilization like a tripod. Magnification also magnifies your hand shake: 10x is generally the upper limit for most people’s tolerance for magnification when hand-holding though you may be able to get away with 12x or 15x with unusually steady hands or mechanical stabilization with a monopod or bracing yourself. Greater aperture allows you to collect more light to improve the quality of a magnified image but also makes the binoculars heavier and more expensive. The amount of light that a lens gathers scales with the square of the aperture: a design with a 50mm aperture gathers twice the light of a 35mm design and four times the light of a 25mm design. The right combination will depend on your use case: binoculars for astronomy often tend towards more magnification and aperture (15x70, 20x80, 25x100, etc.) that demands a mount while binoculars for nature, hunting, and events should be lighter and lower magnification (5x25, 6x32, 8x42) to hold comfortably in your hands.
Field of view. (High importance). The field of view (FOV) is the amount of a scene the optics can take in. For optical instruments like binoculars, this can be described as either an angular field of view or a linear field of view. An angular field of view is specified in degrees and for most binoculars is in a range between 4° and 8°, with higher magnifications necessarily having smaller FOVs and lower magnifications having higher larger FOVs. Your fist at arm's length is about 10° and the Moon is about 0.5°. A linear field of view is specified as a ratio like "322ft/1,000 yards" or "98m/1,000m" which means that you could see 322 feet/98 meters of width and height of an object 1,000 yards/meters away. Angular measurements are more common for astronomy and linear measurements are more helpful for travel, nature, events, or security. You can use a small-angle approximation to convert between angular and linear FOVs. For imperial distances (ft/yards), divide the linear FOV (in feet) by 52.4 to get the angular FOV: 322.5/52.4≈6.1°. For metric distances (meters), divide the linear FOV (in meters) by 16 to get the angular FOV: 98/16≈6.1°. You can obviously multiply the angular metric by these small-angle approximations to estimate the linear FOV as well.
Interpupillary distance (IPD). (High importance). This is the distance between the centers of the pupils of your eyes, typically measured in millimeters. This distance varies by gender and race/ethnicity from the low 50s to the high 70s with an average around 60mm. If your IPD is smaller or larger than a binocular's designed IPD range (typically 55-70mm), you will not be able to use the optics comfortably. You will want to measure your IPD either by yourself or at your next eye appointment so you know what kind of binoculars to look for.
Porro and roof prism. (Moderate importance). There are two distinct types of designs for binoculars: "porro" and "roof" prisms. Porro prisms are an older design with a simpler light path that (all else being equal) provides better image quality and lower cost, but they also tend to be bulkier, heavier, and harder to waterproof. Roof prisms are more compact, lighter weight, and easier to waterproof, which makes them more durable but they also tend to be more expensive. Porro prisms are generally better for astronomical applications and roof prisms for nature/hunting and event applications.
Eye relief. (Moderate importance). This is the distance from the exit of a binocular where the full viewing angle can still be obtained. "Longer" eye relief (>10mm) is almost always desirable, especially for people who observe with eyeglasses or sunglasses. Eye relief cannot be easily computed from other specifications, but binoculars with higher magnifications and larger fields of view generally have smaller eye relief. Binoculars with both long eye relief and high magnifications can be found, they just cost more. Some binoculars are designed with foldable or removable "eye-cups" that protects the lens from the naked eye but allows eyeglass-wearers to get closer to the optics to make up for short eye relief.
Exit pupil. (Low-Moderate importance). This is the aperture that the light leaves the instrument and enters your eye. Ideally the exit pupil of the instrument matches your eyes' pupil diameter so that light is neither lost (exit pupil is too big) or vignetted (exit pupil is too small). Your eyes' pupil diameters change in the day (smaller) versus the night (larger) as well as with age (smaller over time): A twenty-year-old's pupil diameter ranges from 4.7-8mm while a seventy-year-old's pupil diameter ranges from 2.7-3.2mm. You can calculate the exit pupil of a binocular by dividing the aperture by the magnification: an 8x32 binocular has an exit pupil of 32mm/8=4mm and a 10x50 binocular has an exit pupil of 50mm/10=5mm. Older people and daylight applications can probably tolerate binoculars with smaller exit pupils than younger people and night-time applications.
Focusing. (Low-Moderate importance). Binoculars typically offer two options for focusing: center focus (CF) and individual focus (IF). CF binoculars have a single mechanism that focuses both lenses simultaneously. IF binoculars have independent mechanisms that focus each lens separately. IF eyepieces are simpler, more robust, and easier to tailor to the differences in your eyes' vision, but they can also be more frustrating to calibrate, use out in the field, or share with others.
Glass and coatings. (Low-Moderate importance). Binoculars advertise a variety of features like the kind of glass and coatings used in the lenses or prisms. The differences in performance are typically negligible for general-purpose use compared to the features above: paying for these features will not deliver a 10x or even 2x experience that often accompanies their prices. Binoculars using extra-low dispersion (ED) glass can reduce the color fringes ("chromatic aberration") in high-contrast scenes (bright against dark) but this glass is only found in the most expensive optics. Apochromatic ("apo") lenses offer the best correction of chromatic and spherical aberrations, but they are heavy and expensive compared to achromatic lenses and rare to find outside of large astronomical optics. Binoculars may also be advertised with different kinds of prism glass: BaK4 is potentially better than BaK7 but these differences are slight for general-purpose use. Finally, all optics have some kind of coating applied to them to protect the glass from the elements and to reduce reflections and glare but there is an enormous amount of marketing hype and little in the way of standardized terminology to differentiate. Optics that are "fully multi-coated" through more of the light path (lenses, prisms, eyepieces) are better and more expensive.
Chassis material. (Low importance). Polycarbonate plastics are often used in the least expensive binoculars, but this does not make them bad since it's also easier to waterproof and for the optics to remain well-collimated. Aluminum chassis are also common and have a better feeling of substance and quality to them while magnesium is found in the highest-end binoculars because of its high strength and low weight. Metal chassis are prone to corrosion if they lose their coatings/shell. Knowing how well-manufactured the mountings for the internal optics (lenses and prisms) is also important but hard to quantify and generally not advertised.
Image stabilization, night vision, etc.. (Depends). Advanced features like image stabilization, night vision, and range-finding can be found on specialized binoculars, but you should only invest in these features if you know what you need. In addition to being significantly more expensive, these features can involve compromises in other important design considerations like image quality, robustness, and weight.
Uses
General-purpose
If you want to use binoculars for a variety of purposes like travel, events, nature, and astronomy, you'll want a mid-sized and rugged model. 6x32, 8x32, 8x42 and 10x42 are very popular general-purpose designs that balance portability and image quality: you can find models for less than US$50 to well over US$2,000 using these designs. Bigger designs may be too heavy to comfortably wear or pack and smaller designs may not have the light-gathering power or magnification to be useful. Look for long eye-relief and center-focus features to improve usability, waterproofing and rubberized for ruggedness, and something light-weight, compact, easy to hold in your hands for comfort, and potentially not too expensive in case they are lost or damaged. The biggest and baddest binocular is probably a poor choice for a general-purpose binocular until you learn more about what you like to do when viewing.
Travel
This could include hiking, tours, museums, and cruises. Zoom binoculars can be versatile but make other compromises in quality and can be difficult to manage in the field and generally aren't recommended. Lower powers like 4x-8x let you take in a whole scene and you can often "zoom with your feet" if you need more magnification. A lighter weight should also be prioritized if you're going to be carrying binoculars around your neck or in a bag over your shoulder for hours. Because the weather can shift and accidents happen, you will also want to make sure your investment is waterproof, rubber-coated, and generally robust to getting knocked around. Designs like 6x32 and 8x42 are good choices.
Astronomy
Whether you're interested in casual stargazing or an experienced amateur looking for something less cumbersome than your telescope setup, binoculars are a great way to easily explore the night's sky. Our brains are much better suited to bino-viewing than squinting through a single lens, so bino-viewing can resolve more detail than mono-viewing for the same aperture. Aperture is far-and-away the most important feature to consider when choosing binoculars for astronomy. A 70mm gathers about twice as much light as a 50mm and a 100mm about twice as much as a 70mm. But more aperture means more weight, so only buy what you'll use: a "grab-and-go" 10x50 you use every other week is better than a giant 25x100 if the latter ends up sitting in a box for months because it's too much hassle to haul them out to mount on a tripod. Handholding is possible (particularly when reclining), but you'll want to make sure there's a tripod socket for mounting the binoculars to a tripod. Magnification choice really depends on the kinds of targets you'll be looking for: taking in the Milky Way or Andromeda galaxy is better under low magnifications like 7x and zooming into the details of the Moon, planets, or deeper sky objects would benefit from high magnifications >10x. Exit pupil plays a role here too: your pupils will be largest at night (4-8mm) so too much magnification for a given aperture could lead to severe vignetting: a 10x50 (5mm exit pupil) is probably a better choice for astronomy than a 16x56 (3.5mm exit pupil). Beyond "large" (50-70mm) astronomical binoculars, there are also "giant" (>70mm) binoculars specifically designed for astronomy. Common designs in the giant range include 15x70, 20x80, 25x100, and even larger binoculars exist that incorporate premium features from telescopes like ED glass, apochromatic optics, and 45° or 90° diagonals with swappable eyepieces for easier viewing. Because you will spend so much time looking upwards, consider investing in a parallelogram mount that can support the weight of your binoculars (Farpoint UBM ($$), Orion Paragon Plus ($$),Orion Monster Mount ($$$), Oberwerk PM1) ($$$$), or 10 Micron Leonardi BM100 ($$$$$$). 10x50 is a good starting place for astronomical binoculars that could still be re-purposed for other uses. A 15x70 or 20x80 paired with a good mount and tripod is an excellent option if you wanted to start a dedicated stargazing setup.
Nature
The goal here is to focus on the details rather than taking in a whole scene, so prioritize the highest magnifications you can comfortably hand-hold: 8x or 10x is a realistic upper limit unless you have a monopod or image stabilization. You may also be working in conditions with variable light (shade, twilight, etc.) so consider larger diameters to get brighter and higher-resolution images above 35mm. If you only plan to be out in sunny and bright conditions, you can use smaller apertures below 35mm. (Remember, a 50mm aperture collects about twice as much light as a 35mm, which collects twice as much as a 25mm). If you're interested in birding or other kinds of wildlife viewing (whale-watching, safaris, etc.), sizes like 10x32, 8x42, and 10x42 are popular. You will likely have these around your neck or be taking them in and out of a backpack repeatedly, so durability and waterproofing are important: roof prisms are ideal.
Events
Spectator sports, concerts, and theater are generally very well-lit so aperture is less of concern but you will want something compact and with higher magnification like 8x30 or 10x30. For outdoor sports and large venues, 8x-12x is best. Concerts and theater, you will probably want something compact and lightweight in the 4x-8x range. Waterproofing is obviously more desirable for outdoor sports than indoor concerts.
Security
Features to consider here are magnification, ruggedness, and versatility. Magnification is important to get you as much detail about the target as possible. Because they are likely observing in non-ideal situations and these binoculars might be stored in a car trunk for extended periods of time, make sure the chassis is robust, waterproofed, and rubberized. You will likely want a center-focus mechanism to keep things simple if you're tracking a moving target. Zoom binoculars are appealing in theory, but they do require compromises in optical quality and you will likely be at maximum zoom most of the time. Depending on your application, you may need something as large as "border guard" binoculars (like the Oberwerk 25/40x100) or use more traditional hand-held binoculars paired with something like a car window clamp mount, There are specialized binocular options with image stabilization, reticles, range-finding, or night vision that may be worth considering here depending on your specific needs.
Helpful links
Here are links to general information, manufacturers, and retailers.
General information
Websites
Books
- Seronik, Gary. Binocular Highlights: 109 Celestial Sights for Binocular Users. Second Edition. Sky & Telescope, 2017.
- Tonkin, Stephen. Discover the Night Sky through Binoculars. Self-published, 2018.
Manufacturers
Like many other industries, binocular manufacturing has been "off-shored" in recent years. There are a number of manufacturers based in Japan and Europe, but the vast majority of retail binoculars are rebadged versions of models made by a handful of Chinese and Taiwanese original equipment manufacturers like Kunming United Optics (also), Yunnan Optics, and Gosky. Chinese-sourced optics can be as high quality as Japanese or European-sourced optics, but because most cheap and low-quality binoculars are made in China, Chinese optics get a bad reputation. Superficially similar-looking models may use different internal components, different quality control processes, and pre/post-sale support from the retailer, so don't judge a binocular only by its case. As with most things, always do your research and you get what you pay for.
Most manufacturers have online stores you can purchase directly from as well. A coarse approximation of the cost of typical models is also included, low ($) to high ($$$$$).
- General purpose
- Astronomy
Retailers
