A first class binocular shows its real worth when you use it under poor light and weather conditions. Its ruggedness is demonstrated only when it has to stand up under uncommon conditions, such as extreme heat, cold, moisture, or jarring. The full worth of a good binocular is not always apparent at first.

Good binoculars are always a combination of good magnification, objective lens diameter, image quality, size,
weight, durability, and quality. It is sensible and practical to choose a model that is best suited for your particular use. And you must understand that the more quality a factory builds into a binocular, the higher the price tag is.

The more familiar you are with the following definitions, terminology, and features of binoculars, the better the chance that you will purchase the binocular that is right for you.

Listing is in alphabetical order to facilitate your research.

Alignment:
This refers to the precise coordination of mechanical and optical elements with one another. (Also called “columnation”.

Central Focusing Wheel:
The central focusing wheel makes it possible to focus precisely both eyepieces of the binocular at the same time. It also makes it possible to compensate for unequal vision. This is by means of a dioptric correction through the adjustment of one eyepiece, usually the righthand eyepiece.

Coatings:
The evaporation and baking on of extremely thin layers pf substances onto the polished lenses and prisms of optical instruments to reduce reflections and increase light transmission.

De-alignment:
This refers to a shift in the position of the lenses due to blows or jarring. It causes double images and is uncomfortable to use.

Dioptric Correction:
This describes the adjustment of the optical instrument to the varying acuity of different persons eyes.

Exit Pupil:
The exit pupil is that circle of light which can be seen in the eyepiece. Mathematically, the exit pupil diameter is calculated by dividing the diameter of the objective lens by the magnification. For example: a 7x50 scope would be 50mm divided by 7X = 7.1mm. The square of the Exit Pupil diameter is the geometrical Luminosity Factor. This value is meaningless because it says nothing about the actual performance or quality of an optical
instrument.

Eyepiece for Eyeglass Wearers:
An eyepiece for eyeglass wearers has an interval between the last lens and the pupil of your eye. This interval represents the difference in distance between persons with and without eyeglasses who use the binocular. Eyeglass wearers need only turn down the eye-shields to be able to get the full field of view.

Eye Relief:
This is the distance (in mm’s) between the glass surface of the eyepiece and the point in space beyond it, where the image is in focus (the point where the user’s eye must be to see the complete image). See Eyepiece for Eye-glass wearers.

Field of View:
The field of view is an angle, with you at the starting point, and is used to compare the width of view at different distances (usually 1000’ or 1000 m). The closer you are to the object looked at, the smaller the field of view. The farther away the object is, the wider the field of view. This figure is valuable only if you customarily are looking close-up – such as looking at butterflies. See Wide Angle.

Focusing:
Focusing refers to the adjustment of an optical instrument in order to make images at varying distances
sharp and clear. There are two basic types of focusing – individual eye adjustment and central focusing.
Both systems are good. In individual eye adjustment you adjust the right ocular to your right eye and the left ocular to the left eye (this is sometimes called the “military way”). In central focusing you still have two adjustments to make. One adjustment is to make both eyes the same strength and the second adjustment focuses both eyes at the same time. Note: Most makers of good binoculars make binoculars in both styles.

Fixed Focus:
This is done while manufacturing the binocular by cementing lenses in specific locations in the tubes to create a no-focus feature (optical depth of field). Instead of focusing the binoculars to match your eyes, the standard procedure, our eyes must focus to match the optics. This works best if you have 20/20 vision. No focusing adjustments are possible to meet changes in your eyesight. Persons having a vision difference between their left and right eyes would have a problem.

Individual Ocular Adjustment:
In this system each eyepiece is adjusted separately. It is the easiest and fastest way to focus your binoculars.
You simply adjust the right ocular to your right eye and the left ocular to your left eye. Well constructed binoculars will automatically adjust for distance – just as your eyes automatically adjust when you look at something across the street and then look at something a mile away.

Interior Focusing:
With interior focusing the exterior objective and ocular elements do not move and so neither air, nor dust, or
moisture is drawn into the system when you focus the bincular. This feature is usually found only in quality binoculars.