MAGNIFICATION (POWER):
Magnification is the number of times the object being viewed is enlarged. Riflescopes are often identified by two numbers, for example: 6×42. The first number indicates the magnification or the power of the riflescope, expressed by the letter “x”, for times. This means that the object being viewed appears to be 6 times closer than would be seen with the naked eye. 

VARIABLE POWER/ZOOM:
Zoom is the ability of the riflescope to change magnification continuously throughout its design range, providing a low power to high power range. For example, a 6-24x50mm riflescope has the ability to magnify the object from 6 to 24 times. 

Low Power: Eg. 1.5-6×42, 2-7×32.
These riflescopes are ideal at close range and for shooting moving targets. 

Medium Power: Eg. 3-9×50, 2.5-10×50.
These riflescopes are ideal for big-game hunting at medium range. 

High Power: Eg. 6-24×50
These riflescopes are best for target shooting, small-game and varmint hunting. 

OBJECTIVE LENS DIAMETER:
The second number in the reference (i.e. 6×42) indicates the diameter of the objective lens or the front lens. The larger the objective lens, the better the light transmission, thus the brighter the image. 

OPTICAL COATINGS:
Various coating processes on the lenses and prisms will determine the brightness and the light gathering of a riflescope thus providing higher contrast and brighter images. The different types of coatings are: 

Coated = A single layer on at least one lens surface. 
Fully Coated = A single layer on all air-to-glass lens surfaces. 
Multi-Coated = Multiple layers on at least one lens surface. 
Fully Multi-Coated = Multiple layers on all air-to-glass surfaces.

FIELD OF VIEW (F.O.V):
The side-to-side linear measurement of the circular field seen through a riflescope. It is defined by the width in feet of the area visible at 100 yards, or in meters at 100m. The higher the magnification, the narrower the field of view. 

RESOLUTION:
The measurement of the riflescope’s ability to distinguish fine detail and sharpness. 

EXIT PUPIL:
This refers to the size of the small disc of light that exits a riflescope. To determine the size, divide the objective lens diameter by the power. For example a 6×42 riflescope will have an exit pupil of 7mm. (42/6=7). 

EYE RELIEF:
This is the distance a scope can be held away from the human eye and can still observe the entire field of view. Long Eye Relief (LER) reduces eyestrain and provides an extra margin of comfort and safety. 

TUBE DIAMETER:
This refers to the diameter of the body of a riflescope; that portion between the belled ends. 

WATERPROOF/FOGPROOF:
Riflescopes can be O-ring sealed for complete waterproof protection, and fogproof which means that they are nitrogen-purged to prevent fogging inside the optical surfaces. These models are able to keep completely dry inside after immersion in water, thus suitable for all weather conditions. 

PARALLAX:
A condition that exists when the image being viewed through a riflescope is not focused precisely on the reticle. Parallax can be detected by an out-of-focus image or moving image in relation to the reticle as you move your eye left to right, up and down while looking in the scope. Scopes with an adjustable objective or turret provides the advantage of parallax correction. 

PRECISION ADJUSTMENTS:
The windage and elevation adjustments affect accuracy and are used to zero-in on the scope. Windage is the horizontal (left-to-right) adjustment, usually the side turret of the scope. Elevation is the vertical (up-and-down) adjustment, usually the top turret of the scope. Adjustments are usually measured in click value. (1/4 MOA = 1/4” at 100 yards) for finer precision. 

RETICLES:
A reticle is the crosshair or pattern placed within the scope, creating a center point to facilitate aiming at a specific object. Certain reticles can also be used to measure distance.