Binoculars 101

Just as certain items of equipment are essential, in order to properly complete any job, outdoorsmen have their own war chests of accoutrements they wouldn’t think of leaving home without.

While they might not be included in a list of bare necessities, a good monocular or pair of binoculars should be placed on the list of secondary items that any sportsman needs to accomplishment the task at hand.

While the binoculars might not be necessary for you to have a great time outdoors, they will certainly make the trip more enjoyable.

Far from the old bulky, heavy models seen hanging around a German Tank Commander’s neck in a WWII movie, today’s binoculars are compact, much lighter and offer better magnification under lower light conditions than those found in granddad’s day.

As a matter of fact, it’s now possible to find a set of 10-power binoculars that will easily fit into a shirt pocket. Although there are many types and manufacturers of monocular and binoculars on the market, basically all share the same properties: an ocular lens — the lens closest to your eye, and the objective lens — the large ones at the end. Without becoming too technical, lenses bend light rays to a point where they form an image. “Focal length” is the distance from the lens to the point where the rays meet.

Here are some examples of the many types of binoculars available.

The longer the focal length, the more you can magnify something. Logically, this is why the telescopes used by pirates to find choice treasure ships over miles of ocean surface and those used to investigate the heavens at the McDonald Observatory are mass pieces of machinery. However, every lens has a fixed focal length that can’t be changed. You can, though, “bend” the light rays to fool the ocular into believing that its length is much larger than it really is.

A somewhat bit of mysterious binocular jargon is the set of numbers that manufacturers attach to their product, such as “7 x 35,” or “10 x 50.” The first number states the power of the binocular (7 or 10 power), while the second number represents the diameter of the objective lens in millimeters (35 or 50). This is simplified if you decide the approximate distance of those items, which you would like to give the once over.

Another factor to consider when purchasing oculars is that lenses can be coated to increase the transmission of light, but we’ll get to that later.

Manufacturers use prisms in binoculars because without them, you would need a lens with a longer focal length and, thus, a long ocular. But by using prisms you can increase an ocular’s power without increasing the size. Also, prisms erects the image by turning it right side up.

There are two types of prisms: roof — used in straight-line compact binoculars; and porro — used in conventional binoculars, or those with a dogleg shape.

This brings us to the three body styles of binoculars:

European: where the body of the ocular houses the porro prisms and a separate, removable barrel houses the objective lens;

American: which also uses porro prisms, but in one solid body piece. The American style is somewhat sturdier, but a little more expensive to produce;

Compact: wherein a solid lightweight body houses the roof prisms and objective lens.

The power of an ocular — the first of two numbers — measures the amount you’re magnifying something. For instance, a 10X power means you’re magnifying something 10 times. Let’s say you’re looking into the brush or a tree, or an angler who is spying a stickup a 100 feet away. With a 10X binocular the object would look 10 times closer, or 10 feet away.

While it might seem best to always magnify something to your highest ability, the fact is, that the higher the magnification, the more difficult it is to find a distant image in the binoculars. This can often be a large problem for anglers, particularly when the wind is rocking the boat, or for a deer hunter if the north wind is whistling across a canyon.

The second of the two numbers, as stated above, measures the diameter of the objective lens, which is on the opposite end from where you put your eye. Basically, the larger the objective lens, the more light you let into the binocular. The more light, the brighter the image.

Three things affect relative brightness: the power of the binocular, the size of the objective lens, and lens coatings (there’s that word again). The more you magnify an object, the more light you need to maintain the brightness of the object. As you raise the power of the binocular, the lower the relative brightness — unless you also increase the size of the object lens. To make a long story short, the larger the diameter of the objective lens, the more light it will let into the binoculars. This is easier to understand if you think about the amount of light let into a room with a small window or a larger one.

As mentioned, another factor governing how much light is let into a binocular is whether the lenses are coated, the presence or absence of which will greatly affect not only the quality, but also the cost of the binoculars. When light hits a lens or prism, some bounces off and the rest pass through. If you chemically coat the lenses and prisms, they reflect less and allow more light to pass through the binocular. Coated optics refer to a chemical coating on one side of the objective lens system, one side of the ocular lens system, and the long side of the prism.

Fully coated optics means the coating has been applied to both sides of the objective and ocular lens systems, plus the side of the prism. Multi-coated optics means the fully coated optics have an additional chemical coating consisting of more chemicals designed to increase the visibility of a distant object.

Another lens coating is U.V.C. coated optics, which means ultraviolet coating. This means the fully-coated optics have been treated with a special coating applied to one side of the objective lens system to filter out ultraviolet light, which gives the lens a deeper purple color. What all this lens coating jargon means is that with the coating, you can have a smaller objective lens that lets through a greater amount of light.

To put it even more simply, you get what you pay for. Usually, the greater the cost, the better the binocular. Obviously there’s more to it than that, but that bottom-line statement is fairly accurate.

Other Binocular Jargon:

  • Depth Of Field: If you look through a pair of binoculars and focus on an object, the depth of field is the distance of those objects in focus in front of the object, plus the distance of those objects that remain in focus behind the object.



  • Diopter Focus Adjustment: This fine tuning adjustment is particularly necessary for people whose vision varies from eye-to-eye. The diopter focus adjustment is found on the right eyepiece — or ocular — and allows you to adjust the focus for any variation in vision between your right and left eyes. The idea is to close your right eye and focus the left binocular on a distant object. Then close the left eye and adjust the diopter focus adjustment until the object is again in focus. This should never change as long as you are the only one using the binoculars.



  • Eye Cups: There are soft rubber cups around each ocular lens that inhibit undesirable light in front of the magnification, but also keep your eyes at the correct distance from the ocular lens. Usually these can be folded down for people who wear glasses.



  • Fast Focus: A bar, rather than a wheel, at the top of the binoculars that brings an object into focus by depressing the right or left side of the bar rather than turning a wheel.



  • Zoom Binoculars: So-called Zoom binoculars allow you to change the power; i.e., magnification, of the instrument by moving a lever near the ocular lens. Most have adjustable powers that range from 7 to 24. Remember that as power is increased, light is decreased.



  • Waterproof/Fog Proof: Some binoculars are sealed with rubber O rings to make them waterproof. These are particularly good for marine applications.



  • Perma Focus: This also is known as self-focusing. The focus is preset so that everything beyond about 20 feet to 40 feet away always is in focus. These are ideal for tracking fast-moving objects.


Again, basically speaking, the type binoculars assigned to a permanent spot on an outdoorsman’s list of indispensable items should be compact, easy to use, waterproof and sturdy.

Shop The Sportsman’s Guide great selection of Binoculars!

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