Rifle Scope Anatomy: How It’s Built

Click to listen to the audio version of this article.

If you are in the market for a rifle scope, you’ve no doubt viewed the long list of specifications common on optic websites. And those specs can be less than enlightening.

So, to make better optical decisions, let’s look at the various parts of the scope listed in those specs and what they do. Once a shooter understands the anatomy of a rifle scope, he or she can make a better choice for their optics.

Using the EOTECH VUDU X scope in the photograph, let us start at the front of the scope and go backward. This takes the same path as the light, which enters:

The objective lens is a scope’s front lens, the size of which is presented in millimeters and noted after the scope’s magnification, as in 2-12x40mm. The larger the objective lens, the more light enters the scope for cleaner, brighter images.

Depending on the manufacturer and model, the scope’s lenses will have various coatings to improve performance. Commonly, an objective lens has an anti-reflective coating to limit glare and an anti-scratch coating. Other coatings to improve image quality are common, too.

The controls for a scope’s reticle are clustered mid-scope, atop, and along the sides.

The top turret is known as the elevation knob. Each click of it moves the bullet’s point of impact up or down, per the optic’s built-in MOA or MRAD measurement system.

The windage knob is on the right side. Each click of this knob moves the bullet’s point of impact right or left, per the optic’s built-in MOA or MRAD adjustment system.

BTW, MOA stands for minute of angle and MRAD is the abbreviation for milliradian. What’s the difference and is one a better choice than the other? That’s a whole other article, though here’s the summary: it depends!

Next up is parallax adjustment. Parallax is the difference between what appears to be the placement of your crosshairs on a target versus where your shot is actually being aimed. To test for parallax, shift your head slightly while looking through a scope. If parallax is at work, the reticle will change position on the target as your head moves. Not good!

Higher-end scopes, especially ones with magnification levels over 10x will have a parallax control knob, frequently on the left side of the scope’s tube. The knob should allow the shooter to adjust for parallax from 25 yards to hundreds of yards, with the distances marked along the side of the knob.

The brightness control adjusts the brightness levels for scopes that have illuminated reticles. The control is usually found to the left of the parallax control on the same knob or turret.

The battery cap, located at the end of the brightness/parallax control, is found on scopes featuring illuminated reticles. Unscrew the cap to insert/remove the battery.

The removable throw lever is increasingly common in variable-powered scopes, providing leverage for easy movement of an optic’s magnification ring.

The magnification ring operates the optic’s magnification plus shows the magnification level selected. Zoom up the magnification for far-away targets and reverse course for up close target encounters. The higher the magnification, though, the narrower the field of view.

Diopter adjustment time. The diopter is a rotating ring used to bring the reticle into sharper focus. Once set for a specific shooter’s eyesight, the diopter shouldn’t have to be changed. But what if a new shooter gets behind the scope? The diopter will need adjusting for that shooter’s vision.

The ocular lens provides the actual view of the target. Like the objective, the ocular will usually have several coatings to enhance optic performance. Scope specs usually delineate the eye relief range of a particular scope, which is the distance from the ocular lens to your eye.

For example, EOTECH lists the eye relief for its Vudu X 2-12x40 SFP rifle scope as between 3.73- and 3.77-inches. That’s likely very close to correct for most shooters, however, a particular person’s eyesight will determine the actual best eye relief.  

It’s not noted in the photo, but the main tube of a scope holds the lenses, front and back,  and what’s known as an “erector tube assembly” beneath the controls.

Nearly all tubes today are made of aluminum of varying grades and are built in 1-inch, 30mm, and 34mm diameters. Some 35mm options have entered the market, too.

Years ago, 1-inch tubes were the norm for most scopes. You can still find some of these, many of them marketed for rimfire rifles. But for centerfire rifles, the trend is definitely for 30mm and larger tubes.

“Many scope makers have transitioned to 30mm tubes or greater over 1-inch tubes for a variety of reasons,” John Bailey, EOTECH’s vice president of marketing, explained. “First, the larger tube diameter allows more light to come through, which provides a more crisp, clear picture, especially in low light conditions. Secondly, the larger tubes provide greater durability and robustness, as well as additional windage and elevation adjustment range.”

The only negative to the larger tubes? They do weigh more than their 1-inch cousins.

In-store or online, use this article as a handy reference for your next rifle scope purchase. Of course, EOTECH’s INSIDER Brand page on hookandbarrel.com is a great place to start your optic-buying journey. And, like firearms, you can’t possibly own only one rifle scope. There’s a scope or sight for every need under the sun. For more, visit EOTECHinc.com.