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Rifle Scopes - Terms & Definitions

June 11, 2008

Rifle Scopes: Terms & Definitions

When selecting a rifle scope, it's a good idea to be familiar with the terms listed below. Combining this knowledge with your preferences will help you select a rifle scope that you'll be satisfied with for years to come.

The numbers on a scope represent the power, or magnification, and the objective lens size. The first set of numbers represent the power of the scope. Some scopes have a variable magnification range, though. For example, a scope that is noted as 3 - 9x has the ability to change from 3 power up to 9 power.

Fixed magnification scopes have their magnification fixed at one power.

The last number noted on a scope represents the size of the objective lens in millimeters. For example, 3 - 9 x 50 represents a scope with variable 3 - 9 magnification and a 50 millimeter lens.


Larger objective lenses gather more light, resulting in a clearer view and better resolution. They do not increase magnification.

Exit Pupil:
The exit pupil should be as large as the human eye under the same conditions. The pupil changes with change in the amount of light, making it large in low light and small in bright light. To compute the exit pupil size, divide the objective lens size by the magnification of the scope.

Field of View:
Field of view in rifle scopes is expressed as the width of the viewing area as seen at 100 yards. Lower magnification scopes will have a larger field of view.

Optic Quality:
Uncoated lenses will allow over 50% of the light to be reflected. Coated lenses will allow better light transmission (i.e., less light being reflected, more being absorbed), resulting in better clarity. A single coating on a lens means the scope is fully coated. The scope is considered multi-coated if additional lenses are coated. If all lenses are coated with more than one layer, the lenses are considered fully multi-coated.

Parallax is the distortion seen when viewing an object at a distance at which the scope is not sighted in for.

The windage adjustment alters the left to right movement of the scope.

The elevation adjustment alters the up and down movement of the scope.

Rings and Mounts:
A good set of rings and mounts are needed to secure any rifle scope. Loose or poor fitting rings will cause the point of impact to vary.
Being familiar with these terms will result in a more satisfied purchase and you will have a quality scope.
Keith Grable is a sports enthusiast, outdoorsman and the owner of an outdoor sports and recreation website where a large selection of  rifle scopes and accessories may be seen.
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