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Whenever I go shopping for a computer, I always take my son. That is because I don't know the vocabulary or the technology. When the salesman starts talking about a mother board, I ask, "Is there a father board?". RAM? "Will that hurt?", I ask. At this point my son make a zippering gesture across his lips and I have been silenced. Buying binoculars also has a rich vocabulary and technology that needs to be understood. Failure to do the necessary research will lead you to a salesperson where the best you can do is nod your head as he/she answers your questions. In the end you may walk out with a purchase of the salesperson's choice and not yours. So with that introduction let's start the vocabulary lesson!

BINOCULAR FORMULA: All binoculars are given a formula of two numbers
separated by an x. Examples are 7 X 35 or 10 X 42. The first number
indicates power. In the 7 X 35 binoculars the objects you view are seven times
as large as their actual viewing size. The second number is the diameter of the
objective lens, measured in centimeters. The objective lenses are located at the
far end of the binoculars.

Power and magnification are terms that are used interchangeably.

The amount of light gathered by the objective lens is referred to as the
aperture.

PRISMS: Binoculars have two prisms inside. The prisms take the incoming
upside down image and turn it upright.

EXIT PUPIL: The number assigned to the exit pupil is the diameter
of the beam of light leaves the eyepiece as you peer through them at
a lit object. This number can be obtained by dividing the objective
lens diameter by the magnification. You should come up with a number
between 4mm and 8mm.

FIELD OF VIEW: Is a number assigned to the viewing width you see at
1000 feet. This is usually identified in degrees and you can expect
ratings between 5% and 10% which can be converted to between 260 and
520 feet.

EYE RELIEF: This is a measurement (usually from a few millimeters to
25 millimeters or more) of the distance away from the eyepiece where the
image is still in focus. It tells you how far away from your eyes you can
hold the binoculars and still have a clear and complete image.

INTERPUPILLAR DISTANCE: An awfully large word to describe how far apart your eyes are!
Binoculars can usually accommodate an interpupillary distance between 60mm and
72mm.

COATINGS: A substance layered onto glass pieces that reduce the reflection of light.

HOW TO SELECT THE BINOCULARS THAT ARE JUST RIGHT FOR YOU!

Consider how you will

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