Guide to Parallax in Rifle Scopes: Adjustments, Why, My Opinion

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By Dennis Howard •  11 min read

One of the features we routinely include when we review rifle scopes is parallax and parallax adjustments. Many shooters, even some experts, aren’t entirely sure what parallax is or how it works. This article is meant to give anyone a basic understanding of parallax in rifle scopes.

Parallax in a rifle scope is the result of the image created in the riflescope when the image of the target is not on the same optical plane as the reticle. This out-of-focus condition causes the crosshairs of your scope to seem to wander or move off your target when you move your head or eyes even slightly while you are aiming.

The errors induced by parallax when you are aiming through a scope are not significant enough to be noticeable unless you are using high magnification. Typically, parallax errors become a problem when using 8X magnification or above. It is important for anyone using a high-power scope to understand parallax, how it affects your shooting, and how it is corrected.

Understanding How Rifle Scopes Work

To fully understand parallax, you need a working knowledge of riflescopes and how their internal structures are organized and work together. Before we get to parallax, let’s look at a typical telescopic riflescope.

The Guts of Your Rifle Scope

The usual arrangement inside your riflescope has four lens assemblies

Where these lenses are inside the scope is important. The ocular lens is the lens through which you look to sight your scope. The objective lens is the glass closest to your target and is responsible for gathering all the light you see through your scope.

The last two lenses, the focus lens and the magnifying lens, are housed in the erector tube. The erector tube is the center of the scope and is often smaller in diameter than both the objective lens and ocular lens housings.

First focal plane scopes put the reticle in front of the magnifying lens. A second focal plane scope places the reticle behind the magnifying lens. This helps explain why the reticle changes size in a first focal plane scope and remains static in a second focal plane scope

Understanding the internal arrangement of the lenses and the reticle helps explain the parallax issue.

How All the Lenses Work Together

With a basic understanding of how the lenses and the reticle are arranged inside your rifle scope, we can begin to grasp how parallax fits into this picture. We know that the parallax problem is caused by the image of the target not being in focus, or on the same focal plane, as the reticle. Both images may seem crisp and clear, but this difference is critical to the riflescope’s performance.

Riflescopes with parallax adjustment come in two styles.

As you might guess, the method of adjusting parallax errors depends on adjusting the internal focus of the target image in relation to the reticle. The key issue is which lens inside the riflescope is moved to change the focal plane of the target image.

Side focus adjustable riflescopes change the position of the focus lens assembly to bring the target image closer or further away from the objective lens assembly. Side focus adjustment knobs are typically graduated in distances from as little as 10 yards to infinity.

Adjustable objective parallax correction works by moving the objective lens assembly in the erector tube. Much the same as a side focus adjustment, moving the objective lens closer or further away from the target changes the focal plane of the image inside the scope housing.

The Problem You May Have Never Heard About

Parallax is a problem that many shooters have never known about. Unless you routinely shoot at long ranges or you are a precision shooter, parallax probably doesn’t figure into your shooting style much. If you shoot at most normal ranges up to 250 yards, parallax error is not a significant problem. There are several reasons that parallax is not a problem for average shooters and hunters.

Which Type of Parallax Adjustment is Best?

That is a loaded question. Ask it among dedicated long-distance or precision shooters, and you better bring a lunch because the discussion and arguments are going to last a long time. Each side has its opinions and will defend them at length. In brief, both types of parallax adjustment have advantages and disadvantages. When choosing which style of scope is best for you, your needs, expectations, and goals should be the determining factors.

However, before you make that decision, an understanding of these advantages and disadvantages should be clear.

Adjustable Objective Parallax Correction – The Advantages

Disadvantages of Adjustable Objective Riflescopes

Side Focus Riflescopes – The Advantages

Disadvantages of a Side Focus Parallax Adjustment

Do I Need a Scope with Parallax Adjustment?

This is a very personal question and one that doesn’t have a clear black and white answer. Several issues need to be considered before you make the decision to spend the extra money to purchase a scope that allows for parallax adjustments.

To Adjust or Not Adjust. What are the Benefits?

The good and bad of having parallax adjustability on your file scope can be the deciding factors for your purchase. In summary, the benefits of scopes with parallax adjustment include:

There are some disadvantages to a riflescope with parallax adjustments that should be considered.

My Take on Parallax Adjustable Scopes

For me, it boils down to a single factor. Money is usually the tipping point in these decisions. If I can afford the difference in cost, I will always choose a scope with parallax adjustment. Why?  There are several reasons.

In the End, Finding Your Comfort Zone is the Key

Purchasing your riflescope, be it with or without parallax adjustments, is like finding the best boots for your feet. Comfort and fit must be correct, and the choice must meet the uses you anticipate.

I hope this article has given you a better understanding of parallax in riflescopes and helps you make the best decision possible as you shop for your next riflescope. If you have thoughts, ideas, or advice, please share them in the comments section below. We all benefit from your wisdom and experience.

Dennis Howard

A life long hunter, fisherman, and outdoorsman, after surviving a devastating tornado in his home town, he saw the effects on people's lives as they struggled to cope. He built his first bugout bag a few weeks later and has been a dedicated prepper/survivalist since that time. After a career as a fireman, Dennis opened a retail store (FFL approved) catering to the military, law enforcement, and like-minded individuals. The store built their own AR platforms. Furthermore, Dennis was also an NRA instructor in both long gun and handgun as well as a certified range safety officer. Read his full interview here.