How to Choose Binoculars

There are as many varieties of binoculars as there are activities to use them, but at their most basic, each relies on the same three fundamental components:

Eyepieces

Also known as the ocular, a binoculars' eyepiece serves several important functions, the most basic of which is magnifying the image created through the objective lenses. An eyepiece is also largely response for the determining a binocular's overall field of view, or diameter, as well as edge-of-field image resolution, which can sometimes become compressed and distorted because of the lens' curve.

Objective lenses

Given their name because the lens sits farther from the wearer's eyes and closer to the viewing object, objective lenses are found in every pair of binocular and monocular. Their primary purpose is to collect light so distant objects can be viewed in high-resolution. Although, the definition of the image is likely to vary from binocular to binocular. While some lower quality options are manufactured using a single glass element, most are comprised of two. This allows the lenses to refract light better and avoid any instances of false color.

Prisms

If you've ever looked at your reflection through a curved surface, you may have noticed that it's upside down and backwards. Objective lenses work the same way. When light is filtered through the lenses, the initial image is projected upside down and backward. With only an eyepiece to magnify the viewing area, the wearer would be forced to stare at things from an exceedingly uncomfortable angle. However, manufacturers include prisms to make sure that doesn't happen, and the two most common styles are: porro and roof.

Porro prism feature a zig-zag feature and are common on many larger binoculars, while roof prisms offer a straight-line design common in more compact models, like Nikon's Trailblazer ATB 10 x 25 binoculars.

Types

Binoculars have been a valued tool for centuries, and over the years engineers have refined, redesigned and created wholly new models to fit growing demands, both financial and performance. In the market today there are four primary types:

Full-size

These are the binoculars you're likely to see in movies. Big, hulking things, perfect for capturing impressive amounts of light, which make them perfect in low-light situations. As a result of their size, users generally benefit from steadier images and a wider field of view. They're a bit too heavy to take on any serious backpacking trips – unless, of course, you don't mind the extra weight. Mostly full-size binoculars are used for observing wildlife or enjoying seascapes. Their specs generally range from 8 x 42 to 10 x 50.

Mid-size

Consider these the "every man" of binoculars. Not too big, not too small, they're moderately sized lenses allow for above-average light transmission, which means optimal viewing throughout most of the day. Mid-size binoculars are a popular choice for enjoying wildlife and sports use, but they might be a bit heavy for any long distance treks. Their specs generally range from 7 x 35 to 10 x 32.

Compact

Smaller options, like Brunton's Echo compact 10 x 25 binoculars, have become the go-to choice for daytime sporting activities and long distance outings. Their light weight and small size makes them an easily handled accessory. However, compact binoculars are limited in their ability to collect light, and users are likely to become less comfortable with the image during extended periods of use. Their specs generally range from 8 x 25 to 10 x 25.

Monocular

As you can probably guess by the "mono" bit, a monocular consists of a single viewing scope. Smaller and lighter than all of their two eyepiece counterparts, a monocular is a good accessory to have on outings that don't necessarily require a long distance viewing device. Their design makes them very limited in their ability to magnify and provide sharpness, so extended viewing is not recommended.

Understanding Optics

Optics is a blanket term referring to how well binoculars or a monocular collects and distributes light to your eye. Typical devices express optics using two numbers: the magnification x the lens diameter. But there are additional factors to consider, as well.

Magnification

Simply put, magnification refers to how large an object at a certain distance will appear to the viewer. Most magnification factors range from 6x to 10x for handheld outdoor use, with the higher end models usually lingering towards the latter. However, it's important to remember that higher magnification isn't always necessarily a good thing.

Human hands naturally tremble. From the world's most steady surgeon to a 12-year-old halfway through a 12-pack of Mountain Dew, hands being forced still will inevitably begin to shake. For the most part, binoculars aren't sensitive enough to react to the hand's movement. But as magnification increases, viewing correspondingly becomes more difficult, reacting to movement and reducing the user's field of view. At 12x magnification, a slight tremor can seem like an intense earthquake.

Lens Diameter

The second number present in binocular specs refers to the lens diameter, which may also be called the field of view. The size of the diameter largely affects how much light a particular lens is capable of collecting. By that logic a wider lends means more optimal viewing, even in low-light settings.

Exit Pupil

Determined by the previous two attributes, exit pupil is a measure of how bright objects will appear in low-light situations, with a wider pupil amounted to more light. A wide exit pupil, which is more common in full- and mid-sized options, allows images to appear much clearer without a lot of light.

Exit pupil diameters are generally measured in millimeters and can be determined by dividing the lens diameter by the magnification number. So Bushnell's H2O 8 x 25 binoculars would have an exit pupil of approximately 3mm.

Zoom

While most binocular and monocular options offer a static magnification factor, some models are fitted with a zoom feature that allows for multiple magnifications. On the surface, the idea of an adjustable device seems like the obvious option. However, zoom binoculars come with several disadvantages. As users increase the magnification, the field of view correspondingly shrinks, becoming narrower and narrower. At a certain point, which will be unique to the user, the image will be impossible to see, as the narrow view will be even more distorted by hand movement.

Additionally, much like the field of view, increasing the magnification also shrinks the exit pupil. Zoom in too much and the pupil becomes smaller than the human eye is capable of matching – approximately 2mm. At that point, the user will simply be looking at darkness.

Coated Lenses

Many manufacturers have developed lens coatings to affect the amount of light allowed in and the overall brightness of objects. Coated lenses usually mean a higher price tag, but it's worth it if you're hoping for a higher resolution.

Binoculars Based on Activity

Which binoculars you choose to purchase should depend largely on what you're planning to do with them. For instance:

Hunting

Hunters love binoculars because they're a perfect way to scan an area and look for subtle movements and details that may have escaped the naked eye. Magnification factors between 7x and 10x are preferred by most hunters, but higher magnifications can be beneficially if accompanied by a tripod to reduce movement.

Bird Watching

An increasingly popular sport, bird watchers tend to aim for 8 x 42 optic binoculars, like Nikon's Trailblazer ATB binoculars, with extended eye relief and a close focus option. Depending on your own dedication and the species you're hoping to spot, higher magnifications, such as 10x and 12x, can be useful for seeing smaller birds and greater distances. Again, a tripod should be used to minimize shaking.

Concert or Theater

Viewing devices have long since been a staple of the theater, with patrons using opera glasses for front row viewing in last row seats. However, recently, it's become more and more common to see binoculars at Broadway. Of course, concert and theater goers are hauling in bulky large- and mid-sized models, they'd be far too cumbersome. But compact binoculars with a wide angle work as the perfect accessory to dinner and a show. Choice optics are 4 x 30, 5 x 25, 8 x 25, 7 x 18 and 7 x 21, and EMS has several options to choose from, like Brunton's Echo 8 x 25 binoculars.

Water Activities

Keeping steady on the water is about as difficult as staying warm in the tundra, so higher magnifications are not suggested. Mariners tend to favor 7x, 8x and 10x options and look for wider objective lenses. For protection, try finding binoculars that are both waterproof and feature a rubber shell, for protection from the sea's salty air.

General Outdoor Activities

For daytime activities, compact binoculars are generally preferred. Small enough to be stored in a pocket or around your neck, these lightweight options are perfect for a hike or climb. Compact devises don't offer the best light collection, but they make up for it with a wide field of view and decent magnification.