A Simple Guide to Choosing Binoculars

Hikers, campers, explorers, boaters, kayakers - we all enjoy the outdoors for different but similar reasons. Whether you’re looking to get away from the business of urbanization or just wanting to enjoy the scenery of the wilderness, taking time to step away and soak up the view is part of the enjoyment of the outdoors. Many choose to carry binoculars on their pack as a visual enhancing device for sightseeing and spotting wildlife.

When you’re searching for the perfect pair of specs for your trip, you’ll notice that there are many different options available. From magnification to objective lens diameter to exit pupil, here are a few of the details that you’ll want to decide on when choosing your perfect pair of binoculars.

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Design

There are two major types of binocular anatomical setups, but they both contain the same basic pieces. 

• Eyepiece : This is the part of your binocular that provides the actual magnification that the equipment is well-known for.

• Prism : Prisms filter light from the lens to the eyepiece, inverting the image in the same way that your actual eye does.

• Roof Prisms: These are essentially in line inside the optical tubes, and make for a more compact set of binoculars. Roof prism binoculars have straight tubes (the front/objective lens is in line with the rear/ocular lens), and are therefore more compact, an important consideration for the sportsman.

• Porro Prisms: Identified by their offset tubes, these prisms offset the objective lens from the ocular lens. Binoculars with Porro prisms are typically superior to their counterparts when it comes to mid-sized binoculars.

• Lens : The lens - whether objective or focusing - is the piece that gathers the incoming light and directs it back into the shaft of the binocular through the prism. In some models, the lens is split into an objective and a focusing lens with the latter located further into the interior of the binocular.

Features and Options

Now that you have an idea of what comprises your binoculars, you can start to pay closer attention to the finer details, features, and options that accompany different styles.

Size

There are a variety of sizes of binoculars, and different sizes are better for specific outdoor requirements. Here’s a quick run-down:

Magnification Power

You’ll note in the size ranges above that a series of numbers is listed after their general size classification. The first of these numbers (the 10 in 10x50) is the magnification power. A magnification power of 10 means that an object will appear 10 times closer than it would to your unassisted eye.

So for example, if you view a deer that stands 100 yards away from you through 10x binoculars, it will appear as though it were 10 yards away (100 divided by 10). Binoculars with magnification powers any stronger than a 10x will make the image appear unsteady, as it amplifies your hand movements more readily and distorts or blurs images. Common binocular magnifications are 6x, 7x, 8x, 9x, and 10x.

Thus, if you’re bird-watching for instance, a higher magnification power is much more desirable than someone who simply uses binoculars to view wildlife while on a trail in the forest.

Objective Lens Diameter

Now we take a look at the second number in the series of numbers listed by style types (the 50 in 10x50). Measured in millimeters, this is the objective lens diameter. So with the 10x50 example, the objective lens would measure 50mm thick. While it may sound like a bigger objective lens would mean a wider field of view, we’re discussing only the light-gathering capabilities of the lens - not the field of view it can manage.

Since the job of the objective lens is to gather light, the thicker the lens, the more light it can gather. Given the same magnification, the larger the objective diameter, the greater the light-collecting power and, thus, the result is higher resolution and brighter images. This is particularly helpful in low-light situations, so consider objective lens diameter of value if you plan to camp, hike, or explore in the evening or nighttime hours.

Keep in mind that binoculars with a larger objective lens diameter tend to be heavier and bulkier, so they’re not necessarily ideal for hiking trips where space and weight are of a prime. Many who opt for larger objective lenses (like hunters at dusk or astronomical uses, for instance) may choose a monoscope or monocular to compensate for the added bulk. These can be mounted to a tripod or other stabilizing device for added comfort to make up for the heavier weight.

Exit Pupil

The exit pupil can be seen by holding the binoculars at arm's length and looking through the eyepieces. The pencil of light you see is the exit pupil.

Measured in millimeters, the exit pupil size is determined by the binocular magnification and the diameter of the front lenses. It’s thus calculated by dividing the diameter of the objective lenses by the magnification number. So, in our example of 10x50, 50 divided by 10 is 5, which is thus the exit pupil size. For variable settings on binoculars, keep in mind that changing magnification will also change the exit pupil as well (as the math denotes).

While the math is interesting, what does it all mean? Exit pupil indicates how bright an object will appear when viewed in low-light situations wherein a higher number means brighter images. But does a ‘brighter’ image necessarily mean a BETTER image?

Image: http://www.garyseronik.com/

Some may argue that a smaller exit pupil’s ability to dim an image actually increases the image’s contrast, thus creating a better, clearer, crisper image for the viewer in a low-light situation. The image above demonstrates this phenomenon where the smaller exit pupil dims the image but improves the quality. It holds water when you’re goal is stargazing where contrast can make a huge difference in image quality.

Here’s a guideline for what exit pupil sizes to focus on when looking for binoculars:

Relative Brightness

Relative brightness is determined by squaring the exit pupil number (so our example would be 5 squared, which is 25). While relative brightness and exit pupil are related, relative brightness also measures how bright an object appears to your eyes: the higher the number, the brighter objects will appear. This is useful in low-light situations.

Manufacturers of high-end binoculars argue that two binoculars with identical exit pupil sizes may differ in their relative brightness, asserting that a variety of refinements—prism type, lens elements, component quality and optical coatings—all affect relative brightness. So if you’re truly looking for the best binoculars for nighttime viewing, keep the relative brightness number in mind.

Eye Relief

The distance between your eyes and the eyepieces is the eye relief. Binoculars with larger eye reliefs will be more comfortable for users, as you can hold the binoculars further from your face. This is especially important for those who wear glasses (if you wear glasses, look for eye reliefs of 11mm or more). 

Field of View

AT 1,000 yards from where you stand, how much area in feet can you see through your binoculars? This is your field of view, and it’s the width of area - usually in feet - that you can see when looking at an object roughly 1,000 yards from your position. A wide field of view is best to find and identify objects such as birds. Keep in mind that usually a higher magnification power results in a narrower field of view. 

Focus

Most binoculars come with a wheel between the barrels that adjusts the focus on your lenses, and many will even come with a diopter ring to adjust the focus independently on each barrel to account for vision differences between the eyes.

Lens Coatings

Some of the light that passes through the lenses in binoculars is reflected away, reducing the amount of light passing through and, thus, causing the image to appear dark. To reduce reflection and ensure clear, sharp images, coatings are applied. Many binocular lenses will thus come with antireflective coatings to assist with light transmission.

"Coated" means a single layer antireflection coating on some lens elements, usually the first and last elements--the only ones you can see. "Fully Coated" means that all air to glass surfaces are coated. Fully multi-coated lenses reduce the most reflection and increase light transmission.

Water-Proof and Weather-Resistant

Waterproof binoculars typically use O-rings to create a seal to prevent moisture from entering. Waterproof binoculars also prevent dust or small debris from getting in. Obviously, if you plan to take your binoculars on a boat or kayak, you’ll want to opt for waterproof designs. Also, do yourself a favor and invest in a strap to ensure that accidental drops don’t happen in the first place!

Weather-resistant binoculars are not fully waterproof. They are designed to protect against light rain but not submersion. Consider weather-resistant styles if you’re hiking or camping and may experience some rainy weather.

Fog-Proof

Humid environments and dewy mornings can cause your binocular lenses to fog and cloud your viewing. The built-up moisture can also permanently damage your binoculars if it becomes trapped in the barrels. To counter fog, binocular makers have developed methods for replacing the air inside the optical barrels with inert gas that has no moisture content and therefore won’t condense. The method is to purge the oxygen and replace it with nitrogen, protecting it against fogging up of the internal lens surfaces, not the exterior ones.

If you are wiping the lenses of your binoculars, use the same mentality as wiping your sunglasses - only use clean lens wipes, not your shirt!

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Best Binoculars for Your Purposes

With all of these styles and specifications taken into account, you can typically narrow down the specific pair of binoculars that’s best suited for you. If you’re having issues, here’s a good guideline of some typical scenarios that you may find helpful: