How Rifle Scopes Work

Types of Rifle Scopes

A rifle and scope
A rifle and scope
Angela Hill/iStockphoto

Some people confuse rifle scopes with gun sights. A good rule of thumb is that a rifle scope provides some level of magnification, whereas a gun sight doesn't. Both devices help shooters take aim at a target. Some sights are very simple, while others use lenses similar to a scope's lenses. Here's a brief rundown on common sight types:

  • Open sights require shooters to line up two sights on a rifle to aim a shot. The rear sight usually looks like a V or a U. The front sight is a simple vertical projection.
  • Aperture sights are like open sights, but use a ring for the rear sight. You align the front sight within the ring while aiming at your target.
  • Red dot sights project a red dot or other illuminated targeting reticle on top of the image of the target. The dot doesn't project out the end of the sight.
  • Laser sights project laser beams toward a target.

Let's say you're looking at a 5-12x42 scope. What do these numbers mean? The first two numbers tell you the magnification settings for that particular scope. In this example, the scope has a range of 5x to 12x magnification, meaning the image you see through the ocular lens will be at least five times larger than it would appear to your naked eye. This also means the scope you're looking at is a variable scope, meaning you can change the magnification settings. Some scopes are fixed scopes -- you can't adjust the magnification setting.


The number 42 refers to the size of the objective lens: 42 millimeters. The size of the lens will tell you how much light it will be able to transmit to the ocular lens. In general, larger objective lenses can transmit more light. But it's not always critical to have a large objective lens -- you only need a large lens if your scope uses high magnification levels in the 14x to 36x range. For most shooters, a 40-millimeter lens is sufficient.

Military sniper scopes sometimes have very large objective lenses -- something hunters don't need.
Military sniper scopes sometimes have very large objective lenses -- something hunters don't need.
Zsolt Nyulaszi/iStockphoto

The type of scope you need depends on the kind of target you plan to shoot. If you plan to hunt big game at a distance of around 100 yards (91.4 meters) or less, you won't need a high-power rifle scope. Anything more than 7x or 8x is unnecessary. If you'll be shooting from a greater distance, you'll need a more powerful scope. For example, if you'll be more than 200 yards (182.9 meters) away from your target, you'll need a scope in the 12x magnification range.­

Obviously, the terrain around you will help determine how far away you'll be from your targets. In heavily-wooded areas, you won't be able to see as far as you would on an open plain. If your preferred hunting grounds are dense forests, you won't need a very powerful scope.

You can even find special night vision scopes that incorporate an infrared illuminator. If the game you want to hunt is nocturnal, a night vision scope might be your best option. Learn more in How Night Vision Works.

After purchasing your scope, you'll need to attach it to your rifle. Let's take a look at the process of mounting a rifle scope.