What is the difference between a gun sight and a scope?

Open sights! Aperture sight! Peep sight! 5-12x42! Fiber optics! Tritium! Variable scope! Night scopes!

What are all these things, how do they work, and when would I want to use what? Some are confused by the difference between a sight and a scope, as well as the different types of each. We’ll do a quick rundown of the different kinds of sights and scopes and their primary purposes, as well as when one may want to change from one to another.



Also called “iron sights'“, open sights are the most basic. They are what we see on all guns before any modifications are done. There is typically a single front post at the end of the barrel, appropriately named the front sight. The rear sights have a double-sight configuration with a gap between them. Aiming is achieved by viewing the front sight through the gap in the rear sight. Actually, this is the method of aiming for most sights we’ll be exploring below.

Open sights are the most basic of the sight group and come standard on pistols, rifles, and shotguns. Some may have distinct designs to differentiate them from others (Glock sights illustrated below), but their function is the same. These are best suited for situations where there is plenty of light, whether outdoors or at an indoor range.



Also known as a peep sight, the aperture sight is similar to the open (iron) sight, but only in the front. While it uses an open front sight, the rear sight is a ring or circular opening to ‘peep’ through while aiming. The concept is that the eye will more easily align the front sight when looking through the rear aperture.

This type of sight is used mostly on rifles. The standard issue M16A2 that I used while serving in the United States Army was equipped with a peep sight. These are also well-suited for daylight use, or in other situations where the light is sufficient for the unaided eye to see clearly.

M16 Rear Peep Sight

M16 Rear Peep Sight

Aligning a shot Through the Aperture Sight

Aligning a shot Through the Aperture Sight


Other Types of Sights

There are many other types of sights that are available to upgrade your gun if so desired. One of the most common is an upgrade to a fiber optic, or FO, sights. Aligning a FO sight is not too different from lining up iron sights or aperture sights: the fron sight is viewed through the rear sight. The difference is in the material the sights are made of. While still being open, and even based on iron (or other composite material), FO sights contain short pieces of optical fiber for the dots. These fibers gather the ambient light around them and focus them toward the shooters eye, making it easier to align the sights even in dimmer light environments.

Fiber sights don’t work light night sights, though. They require existing light to gather and focus. Tritium is a substance used in open sights to allow alignment even in the dark. Tritium has been used in various household items, including wrist watches, to illuminate in the dark. Again, as with iron sights, the front sight is aligned through the rear sight. The only difference is these can be seen in the dark and are designed to be used in low- or very-low-light conditions.

Red Front and Green Rear FO Sights on a  Springfield XD

Red Front and Green Rear FO Sights on a Springfield XD

Tru-Glo TFX , a Combination of Fiber Optics and Tritium for Day and Night

Tru-Glo TFX, a Combination of Fiber Optics and Tritium for Day and Night



First, we’ll go over what all scopes have in common. Scopes are separate devices that are mounted onto a firearm. They use lenses to magnify the view of the shooter, just like a telescope, a microscope, or a magnifying glass. They give the shooter a sharper view and increased ability to see and aim at a distant target.

Scopes are measured in magnification levels and lens diameter. A scope that is designated 5-12x42 will magnify the image seen through it from 5-times to 12-times the normal size. The 42 designates the diameter of the objective - or front - lens, which gathers light and focuses to the rear - ocular - lens. There are also scopes that don’t ‘zoom’ as the example above but are fixed with only a single magnification.


Night Vision Scopes

And finally, the most fun of all! Night vision scopes provide just that — the ability to see at night. Where the fiber and tritium sights give the shooter a view of where the sights are, night vision truly allows the shooter to see not just the scope but the environment being viewed through the scope. Without getting too technical, there are two types of night vision technology: Image Enhancement and Thermal Imaging. Image enhancement captures light and amplifies it while thermal imaging captures the heat signatures and presents them to the viewer. There’s a more detailed article here.

A popular use for these is for varmint hunting, or rifles used to hunt down varmints such as coyotes, rats, or other critters that damage crops, livestock, or other property. Because they are mostly nocturnal creatures the night is the most favorable time to clear them from the property.

A view through a night-vision scope.

A view through a night-vision scope.


This is, of course, a very basic, high-level view of sights and scopes — and we haven’t even begun a discussion on holographic or reflex sights! There are as many flavors and combinations of flavors as there are shooters, as well as after-market manufacturers and marketers that offer anything and everything you could ever want. Don’t like what you have? Pop ‘em off and get something new. Don’t like them either? There’s a sight for that!