This article is to introduce some of the terminology used in talking about rifle and handgun scopes. This article does not include everything because some manufacturers make things and gadgets that only are put onto their scopes. This article is not to compare which scope is better or what-not. This article attempts to cover some of the basic terms used. Everything is correct to my knowledge from research. For Information purposes only.
First there are 2 types of scopes, fixed power and zoom. A fixed power scope is set at one magnification. For example, a 10X scope is a 10 power magnification scope. This scope can magnify your normal vision 10 times. The second type is the zoom power scope. These scopes are able to adjust the magnification from one power to another. For example, a 3X-12X scope is able to zoom from 3 power, to 4 power, to five power, etc., all the way to 12 power.
Tube Diameter-This is the size of the body of the scope. The bigger the tube diameter, the more light is able to pass through the scope.
Objective Lens-The objective lens is the "business end" of the scope. It is the first lens that gathers light for the trip into the tube. Again, bigger is better. The bigger the objective lens the more light that can be gathered. The higher the magnification, the bigger the Objective Lens must be. This is because the light must travel through more lenses and usually travel further through the scope. on some scope the objective can be adjusted for clarity.
Lens Coatings-A good scope has a metallic type coating on all of the glass surfaces to increase light gathering. This process is very exact and a scope with all of it's glass coated will be more than a non coated scope. Bullet Drop Compensator (BDC)-A BDC is usually an elevation changing dial or knob on the scope. These enable the shooter to aim dead on without having to raise or lower the weapon when estimating elevation. The shooter simply dials in the correct range and the BDC compensates for elevation. The shooter puts the cross hairs on target and fires. Think of it as throwing a baseball. The most accurate way to throw is in a straight line. But, if you want to throw a long distance you must estimate and throw the ball up at an angle for it to reach the target. If not, the ball will fall short.
These have been some of the basic terms used in scope terminology.