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The numbers (nn x nn)
The first number is the magnification. This number tells you how many times closer an object will appear when viewed through the binocular. The second number indicates the diameter of the front lenses in millimeters. The larger the front lens diameter, the more light they will let in. Larger numbers don't always mean higher quality.
Field of View (FOV)
The area seen from left to right through the binoculars at the specified distance. It is usually expressed @1000 yards/meters. Generally the lower the magnification the wider the field of view. If you are going to be using the Binoculars to view things that are moving, a wider field of view may be more favorable. If you are going to be observing stationary or slower moving objects, a higher magnification and narrower FOV would be acceptable.
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Designs The two basic design types of binoculars are Porro Prism and Roof Prism. Porro prism binoculars have large lenses in the front and small lenses in the back. The front and rear lenses are offset. Roof prism are designed with both sets of lenses aligned in the same barrel. Porro prism binoculars are generally brighter and less expensive. Roof prism designs are more costly but usually tougher. |
Center or Individual systems are commonly found in binoculars. Center focus binoculars have a center mounted wheel that simultaneously focuses both sides. Individual focus binoculars have individual adjustments on each side. Individual focusing is popular in Military and Marine binoculars. High end center focus binoculars will provide some type of diopter adjustment to compensate for differences between your left and right eye. A close focusing binocular allows you to view closer objects more clearly
Eye Relief
The eye relief determines how far your eye can be from the binoculars while still allowing a full FOV. Eyeglass wearers would want a high Eye Relief design.
Exit Pupil
The exit pupil is the bright circle of light that appears in the rear lens when the binocular is held away from the eye. The diameter of the exit pupil in millimeters is equal to the front lens diameter divided by the magnification. All other things being equal, the higher the number the brighter the binocular.
Armoring
Rubber or polyurethane coating that makes the binoculars more resistant to damage. The armoring helps eliminate noise caused by contact with other objects. If water proofing and noise reduction is important, Armoring should be a consideration.
General
Factors to consider are magnification, brightness, size, environment, and cost. If you are going to be viewing long distances or want to see greater detail, select binoculars with a 10x or greater magnification. For average use, 7x or 8x should be adequate. Higher magnification binoculars are usually larger and sometimes allow less light. Lower magnification models tend to have a wider FOV and make it easier to view motion. Look for a large objective lens if you will be in low light. Larger binoculars are generally easier to hold steady and offer a brighter image than compact binoculars. Be aware of the primary use for the binoculars. Some people have found the need more than one pair. While price should be kept well in mind, remember that binoculars are something that you may will have for the rest of your life.
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