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What exactly is parallax in a scope? How can a scope be parallax free?

Jul 25, 2023

Have you ever encountered a situation where the point of impact of each shot landed in a different location during the use of a scope? Many people blame this on technical issues or scope mounting problems, but in reality it’s more likely to be due to parallax.

What is parallax?

Wikipedia explains parallax as the difference in direction that results from looking at the same target from two points that are a certain distance apart. What is parallax in a scope? Let’s take a simple example to make it easier to understand.

As shown in Picture 1, when two objects are placed on different planes, object A can completely cover object B when viewed from directly in front, but with a slight change in viewing angle, object A and object B no longer coincide. This is due to the presence of parallax.

In Picture 2, two objects are placed on almost the same plane or even coincide; when viewed from directly in front, object A is perfectly coincident with object B, and when the viewing angle is changed, object A is still coincident with object B. This is the parallax-free meaning.

Translated to the riflescope, object A and object B become a reticle and an image (Picture 3). Parallax occurs when the reticle and image are not in the same plane, while parallax-free means that the reticle and image are almost in the same plane.

The presence of parallax in the scope has an effect on the accuracy of the shot.

Combining Picture 1 and 2, we replace objects A and B with a reticle and an image (Picture 4). When the reticle and image are not in the same plane, the center of the reticle will only aim at the target when viewed directly in front of you. As soon as we change the angle or move the head or eye position slightly, the position of the center point aiming will change, and therefore the point of impact will also change.

When the reticle and the image are almost on the same plane, the center of the aiming point is always locked on the target no matter how we change the angle or move our head or eye sight, ensuring the accuracy of the point of impact.

Parallax exists and free parallax scope expalined

So how do we eliminate parallax in the use of scopes?

Theoretically, we can achieve parallax-free by simply adjusting the imaging position to be almost in the same plane as the reticle.

AO(Adjustable Objective) Adjustment scope, side focus scope and fixed focus scope

Scopes can be divided into three categories based on the type of focusing. In Picture 5, on the left is an AO (adjustable objective) riflescope, which allows you to change the focus by fine-tuning the position of the objective lens; the center is a side-focus riflescope, which changes the focus by adjusting a lens in the riflescope that is specifically designed for focusing. Both are effective in eliminating parallax.

To ensure accuracy, it is necessary to eliminate parallax by focusing before each shot and after changing the shooting distance.

The last type of scope is a fixed focus scope, which means that there is no AO (adjustable objective) focus or side focus, and is generally factory set to be parallax free at 50 or 100 yards. In general, fixed-focus scopes are suitable for everyday use at low magnifications (such as our bestselling S6 1-6X24 LPVO scope), because the higher the magnification, the greater the likelihood of parallax. On the other hand, precision shooting, LR, XLR and competition will require the first two types of quality scopes that can be focused.

So if you are a big fan of medium to long range shooting, it is highly recommended to bring home the Victoptics S4 series, which has a great side focus parallax knob like the one pictured below. And if you combine it with a big side wheel, the parallax adjustment will be more precise to help you win the game.