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Binoculars Information - How to Understand the Numbers on the Binoculars?

Binoculars Information - How to Understand the Numbers on the Binoculars?This page is a supplement to our How to choose binoculars article.
Binoculars always come in handy - whether you're an avid hunter or an occasional theater-goer. Binoculars are essential gear for camping and hiking, a day in the field or a vacation trip to the grand canyon. Choosing the best binocular for your needs isn't always easy. Consider when, where and how often you plan to use them in order to select a binocular with a combination of features that are right for you.

TERMINOLOGY
1. DIOPTER ADJUSTMENT
2. OCULAR LENS ASSEMBLY
3. PRISM SYSTEM
4. FOCUS SYSTEM
5. HINGE
6. OBJECTIVE LENS
BINOCULAR MAGNIFICATION (POWER)
Binoculars are often referred to by two numbers separated with an "x". For example; 8x32. The first number is the power or magnification of the binocular. With an 8x32 binocular, the object being viewed appears to be eight times closer than you would see it with the unaided eye.  We do NOT recommend to use binoculars with magnification over 10x without a tripod - if you go with too much magnification in a hand-held binocular, your image will be very shaky! Also, many people ask - How far can you see with a binocular? - we always answer - You can see as far your eyes can see, but the objects will seem to be closer - magnified by the power of your binoculars. Please see this page for some sample digital pictures taken through giant Oberwerk binoculars with 25x and 40x magnification.
OBJECTIVE LENS SIZE (APERTURE)
The second number in the formula (8x32) is the diameter of the objective or front lens. The larger the objective lens, the more light that enters the binocular, and the brighter the image.

 

Binocular
A binocular consists of two optical systems that are joined by a hinge and (typically) share a common focusing mechanism. The ability to create an image for both eyes simultaneously provides a realistic perception of depth. Binoculars are available in a great variety of sizes, magnifying powers and features to suit any purpose or preference.

TYPES OF BINOCULARS
Standard Binoculars -
A standard or full-size binocular can be used for everything from nature observation to spectator sports.
Compact Binoculars -
Compact Binoculars are smaller and lighter in weight and are a good choice to take along to the theater or concerts or on hikes and hunting trips.
Wide angle Binoculars -
Wide angle Binoculars are ideal for tracking fast-moving action across wide areas such as football fields, racetracks and wilderness terrain.
Zoom Binoculars -
A zoom binocular allows the user to increase the magnification in order to focus in on the details. From distant to near view, it's the best of both worlds.
Waterproof Binoculars -
Waterproof Binoculars deliver clarity despite foul weather conditions including fog, rain and ice. O-ring sealed and nitrogen purged for reliable fogproof, waterproof performance.

Coated Optics
Lens surface coatings reduce light loss and glare due to reflection for a brighter, higher-contrast image with less eyestrain.

TYPES OF COATINGS
Coated - A single layer on at least one lens surface.

Fully Coated - A single layer on all air-to-glass surfaces.

Multi-Coated - Multiple layers on at least one lens surface.

Fully Multi-Coated - Multiple layers on all
air-to-glass surfaces.

PC-3? Phase Coating
Found on the best roof prism Binoculars, this chemical coating is applied to the prisms to enhance resolution and contrast. Would not provide an advantage on porro prism models.

Diopter Adjustment
A "fine focus" adjustment ring usually provided around one eyepiece to accommodate for vision differences between the right and left eyes.
Exit Pupil
Refers to the size of the circle of light visible at the eyepiece of a binocular. The larger the exit pupil, the brighter the image. To determine the size, divide the objective lens diameter by the power (an 8x32 model has an exit pupil of 4mm).
EyeGlass Wearers - Eyecups
Binoculars come with Twist-Up, Pop-Up or soft rubber Fold-Down eyecups which go down for eyeglass wearers. These options allow everyone to see the entire field of view.
Eye Relief
The distance a binocular can be held away from the eye and still present the full field of view. Extended or long eye relief reduces eyestrain and is ideal for eyeglass wearers.
Field of View (F.O.V.)
The side-to-side measurement of the circular viewing field or subject area. It is defined by the width in feet or meters of the area visible at 1000 yards or meters. A wide angle binocular features a wide field of view and is better for following action. Generally, the higher the magnification, the narrower the field of view.

Focusing SYSTEMS

TYPES OF FOCUSING SYSTEMS
INSTAFOCUS? - A paddle or rocker bar between the
barrels adjusts the lenses allowing for rapid focusing adjustment. Ideal for following subjects in motion.

Center Focus - A focus wheel between the barrels moves the lenses.

PermaFocus? - Does not require focusing. The optics are preset and optimized for distant subjects and fine focusing is achieved via the user's eyes.
I.P.D. (Inter-Pupillary Distance)
The distance between the eyes differs from person to person. The adjustment for this difference is accomplished by opening or closing the hinged portion of the binocular to bring the eyepieces closer together or father apart.
Light Transmission
Refers to the efficiency of an optic, or its ability to deliver the maximum amount of the light entering the objective lens to the eye.
Magnification (Power)
Binoculars are often referred to by two numbers separated with an "x". For example: 8x32. The first number is the power or magnification of the binocular. With an 8x32 binocular, the object being viewed appears to be eight times closer than you would see it with the unaided eye.
Objective Lens Size
The second number in the formula (8x32) is the diameter of the objective or front lens on binoculars. The larger the objective lens, the more light that enters the binocular, and the brighter the image.
Near or Close Focus
The shortest distance at which the binocular is capable of providing a sharply focused image of an object. Especially of interest to birdwatchers and nature buffs.
Prism Glass
Most optical prisms are made from borosilicate (BK-7) glass or barium crown (BAK-4) glass. BAK-4 is the higher quality glass yielding brighter images and high edge sharpness.
Prism SYSTEMS
The prism system of a binocular reduces the size needed to provide focal length and turns what would be an upside-down image right-side-up.
There are two types of prism systems, roof and porro.

TYPES OF PRISM SYSTEMS
Roof Prism Binocular System - In roof prism Binoculars the prisms overlap closely, allowing the objective lenses to line up directly with the eyepiece. The result is a slim, stream-lined shape in which the lenses and prisms are in a straight line.
Porro Prism Binocular System - In porro prism Binoculars the objective or front lens is offset from the eyepiece. Porro prism Binoculars provide greater depth perception and generally offer a wider field of view.
RAINGUARD?
With Rainguard, Bushnell's permanent, patented, hydrophobic and oleophobic lens coating, a foggy view is no longer an issue. This unique coating acts on water drops from rain, snow, sleet and even your own breath, reducing them into much smaller droplets. These tiny drops scatter less light, ensuring a clearer, brighter view.
XTRTM technology
As light passes through the many prisms and lenses of a roof-prism binocular, some light is usually lost along the way. Bushnell's exclusive XTR technology - utilizing 60 layers of coating on each prism - conserves, harnesses and optimizes the available light. XTR delivers an amaizing 99.73% light transmission of 90%, making binocular the brightest in its class.
Resolution
Resolution, or definition, is the ability of a binocular to distinguish fine detail and retain clarity.
Waterproof/Fogproof
Some Binoculars are O-ring sealed and nitrogen-purged for total waterproof and fogproof protection. These models can withstand complete immersion in water and stay dry inside. The interior optical surfaces won't fog due to rapid temperature change or humidity.
Zoom Binocular
A binocular with a variable power range, for example: 8-20x. Magnification is changed with a convenient lever or knob allowing you to increase the magnification when you want to get in close for detail from a distance.
Bushnell Binoculars Manual is available for download here
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