Binocular Buying Guide

This guide has been compiled to aid you to better understand the jargon surrounding binoculars and so help you choose the right pair of binoculars for you.

What the numbers mean

Numbers are used to indicate binocular specifications, for example 8x40. The first number is the magnification. This number tells you how many times larger or nearer an object will appear when viewed through the binocular. Eight times larger than with the naked eye in our example. The second number indicates the diameter of the objective lenses in millimeters (40mm in our example). The objective lenses are the large lenses at the front of the binocular. The larger the objective lens diameter the more light it can transmit back to the eye. Higher numbers don't necessarily mean better binoculars. Magnification and light gathering power should be determined by your application.

Zoom binoculars are also available, for example 7-15x24, where the magnification can be varied from 7x to 15x.

Field of View

The width of the area (in meters) seen through the binoculars at a specified distance (usually 1,000 meters) is the field of view. Generally the lower the magnification the wider the field of view. Binoculars with a wide field of view make it easier to scan large areas or follow a moving object.

Exit Pupil

The exit pupil is the bright circle of light that appears in the rear (ocular) lens when the binocular is held away from the eye. The diameter of the exit pupil in millimeters is equal to the front (objective) lens diameter divided by the magnification. 5mm in our example above. All other things being equal, the higher the number the brighter the binocular. An exit pupil of at least 6-8mm is recommended for low light applications.

Interpupillary Distance

The distance between the binocular's exit pupils, which are adjustable to suit the indervidual.

Eye Relief

The eye relief determines how far your eye can be from the eyepiece while still allowing a full field of view through the binocular. This is important to eyeglass wearers who should look for a High Eye Relief design. In most binoculars the eyecups can be folded back to aid spectical wearers.

Design Types

There are two basic design types of binoculars: Porro Prism and Roof Prism (also called Dach Centre Focus or DCF).
Porro prism binoculars are the conventional type with large lenses in the front and small lenses in the back. The front and rear lenses are offset.
These come in two types:
  • Mini Centre Focus (MCF) - Compact design havig the ojbective lenses closer together than the eyepieces.
  • Zeiss Design Centre Focus (ZDCF) - A design havig the ojbective lenses further apart than the eyepieces.
Roof prism binoculars are designed with both sets of lenses aligned in the same tube, like two telescopes side by side.Porro prism binoculars are generally brighter and less expensive. Roof prism designs are more expensive but usually more robust.

Focusing

Center and Individual are the two focusing systems commonly found in binoculars.
Center focus binoculars are equipped with a center mounted wheel that simuntaneously focuses both tubes.
Individual focus binoculars have individual adjustment rings on each eyepiece. This allows separate focusing of each tube. This system is popular in Military and Marine binoculars.
Quality center focus binoculars provide some type of diopter adjustment to compensate for the small difference between the viewers right and left eyes. Minimum Focus Distance is also a consideration in binocular selection. A close focusing binocular allows you to view objects closer in in sharp detail.

Diopter Adjustment

Because the left and right eyes are rarely exactly the same, a balancing focus adjustment is provided.

Coating

This is an ultra-fine chemical deposit on the lens surface that cuts down reflections reducing light loss and flare.
"Coated Binoculars" usually means only the outer surfaces are coated.
"Ruby Coated Binoculars" Red/Orange coating to reduce UV haze over long distances.
"Multi-coated Binoculars" One or more lens is coated with several layers.
"Fully Multi-coated Binoculars" Every lens in the binocular is coated with several layers.

Armoring

Armored binoculars are covered with a rubber or polyurethane material that makes them more resistant to impact damage and scratches. The armoring helps eliminate disturbing noise caused by contact with metal objects. Most armored models are easier to grip and provide better resistance to the elements. Check the specifications if water proofing/resistance is important. Water resistant models are not damaged by humidity or light rain. Water proof binoculars can actually be submerged without damage.

Compact Binoculars

Compact models are smaller and lighter than conventional binoculars. A lightweight roof prism design allows some 8x and 10x models to be easily carried in a pocket. This is a considerable advantage for hikers, sports enthusiasts, or anyone desiring good performance in a small package.

Image Stabilization (IS)

Designed by Canon to allow the use of higher magnification binoculars whilst cutting down on image movment.

Selecting the Right Binocular

Choosing the right binoculars for you is not a difficult task. Some factors to consider are magnification, brightness, size/weight, exposure to the elements, and price.
First decide what your primary use will be. If you are viewing at long distances or want to see greater detail you may want to select a binocular with a 10x or greater magnification. For moderate distances a 7x or 8x may be more useful. A higher magnification binocular is usually larger and heavier and sometimes less bright. Lower magnification models tend to have a wider field of view and make it easier to keep an object in view while in motion, on a rocking boat for example. Look for a large objective lens if you work in low light, as in viewing at dawn or dusk.
Larger binoculars are generally easier to hold steady and offer a brighter image than compact binoculars. They are however, less convenient and heavier.
Your primary use will determine the best balance of these factors. You may find that your needs are so diverse you need more than one pair. Remember when considering price, you are investing in a quality optical instrument that will give you many years of viewing pleasure.

 

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