What Is Parallax on a Scope? (How to Adjust and Correct)

Parallax is a common yet misunderstood phenomenon that can happen to every shooter using a scope. It is often seen as a moment when the scope’s reticle appears to be moving erratically as shooters try aiming.

This phenomenon is due to the reticle and target image not being on the same focal plane within the scope. Fortunately, there are pre-built features in modern scopes and techniques that can reduce or even eliminate this effect.

This guide will explain what parallax is on a scope, how to correct it, and answer additional questions surrounding it.

What Is Parallax on a Scope?

Parallax is a phenomenon wherein the reticle appears to be moving across the target as the shooter’s eye moves away from the optical axis, swimming away from what you are trying to aim at.

The phenomenon can hinder your accuracy, as you will not be able to get your crosshairs online with your target to be able to hit it. When this inaccuracy happens, your reticle and point of aim will not be in the same place.

The parallax effect occurs when the reticle and target are on different planes of the scope. This will depend on how far you are from the target and tends to be a problem only on higher-power scopes (the higher in magnification you go, the worse it can get).

This is due to the projected sight picture being far from the reticle due to magnification, which causes the reticle distortion.

That said, this effect can be diminished with a consistent cheek weld onto the scope. You would also need to recalibrate your sight until the reticle goes where it should, using several adjustment methods.

Parallax Adjustment Mechanisms

External parallax adjustments, also known as adjustable objectives or side focuses, are typically available for high-power scopes where users are most likely to experience parallax.

There are three methods for eliminating or at least minimizing the misalignment of the image and reticle by aligning the scope.

1. Parallax Adjustment Turret: On the left side of your high-powered rifle scope, you will find a side-focus knob that will allow you to focus the internal lens, countering parallax development.
2. Factory-Set: Also known as fixed parallax, some manufacturers set a built-in parallax-free zone of around 50-100 yards where users will experience no parallax.
3. Adjustable Objective (AO): Another adjustable feature would be the objective bell or dial that controls the clarity of the objective lens.

Step-by-Step Guide to Correcting Parallax

Here is a step-by-step guide for any shooter looking to correct their target and reticle view, aligning them on the same focal plane and eliminating Parallax within their optics.

Step 1. Set Up Your Rifle

Before you shoot, ensure your rifle is positioned on a stable platform, such as a sandbag, to minimize any apparent movement when fine-tuning.

Step 2. Choose a Known Distance

For long-range shooting, select a fixed target distance of 100 yards and attempt to focus on your target.

Step 3. Set Parallax Adjustment to Infinity

If your scope has a focal adjustment knob, turn it all the way down to the infinity setting (marked with a  ∞ symbol).

This will often be enough to eliminate parallax at the distances most hunters and long-range shooters plan on engaging in.

Step 4. Aim and Obtain a Sight Picture

Look through the scope and align your reticle with your target. Then, move your head up and down slightly without moving the rifle.

Ensure that your view of the target is clear and complete and that your head position is comfortable with a solid cheek weld and enough eye relief.

Step 5. Adjust Parallax for Clarity

If you are accounting for shorter distances, adjust the knob or turret for closer distances so that you can focus on the target without the reticle moving unpredictably.

You would want to have the clearest image of your target regardless of distance.

Step 6. Check for Reticle Movement

When you move your head, note where your reticle appears to sway freely and adjust the parallax with your side-focus knob.

If your reticle moves downwards, twist the knob for a closer distance setting. If your reticle is moving upwards, set it for a farther distance.

After calibration, repeat moving your head until there is no movement from the reticle, meaning the position is parallax-free.

Step 7. Fine-Tune Parallax Adjustment

Continue testing parallax adjustment until the reticle crosshairs remain at the center of the target despite your head positioning.

Step 8. Find the Parallax-Free Point

Parallax-free scope means that regardless of eye movement or head-side movement in relation to the axis of your reticle, the image remains in place.

You can adjust the parallax with your side focus or other mechanisms listed above to ensure parallax-free shooting at every distance.

Step 9. Confirm by Shooting

After adjusting your sight, you can shoot a few rounds to verify your aim is error-free at the correct distance.

There must be consistent shot placement from your bullet’s point of aim, and your reticle should not float around even when moving your head around.

Step 10. Lock in the Parallax Setting

Some scopes have a locking mechanism to secure your focal adjustment and prevent any unnecessary changes before you shoot.

Step 11. Recheck If Necessary

Whenever someone else uses your rifle or if it gets dropped, always check for any changes or parallax, then adjust with your side focus adjustment.

The Importance of Focal Plane Alignment

When you shoot with a scope, your scope simplifies aiming by lining up the reticle with your target before firing. However, with parallax, you need to refocus your sight to ensure that everything is on the same focal plane.

As stated, the phenomenon occurs whenever your reticle and target are not on the same focal plane within the scope. This separation is as if the target and reticle were written on two sheets of paper instead of one.

Perfect eye alignment is one way to remedy this issue. The reticle will continue moving about unless you aim perfectly down the center, in which case your head, lenses, reticle, target image, and target are all aligned.

That said, staying perfectly still and center is quite tricky, which explains the importance of focus adjustment. This forces the reticle and image from different planes to coincide for increased accuracy.

Whether you are using a first focal plane or a second focal plane scope, ensuring your gear is on a single plane will significantly reduce inaccuracies and increase shooting speed.

Parallax Concerns at Different Distances

Ensuring a clear reticle is always the starting point when setting your scope, but you would need to repeat the process in relation to different distances.

It would help if you always conduct your focus adjustment whenever your shift ranges, as the settings for short- and long-range shots will differ.

The average big game hunter may not notice the inaccuracy due to their proximity to their prey. However, a precision shooter would want to focus on different shooting distances, which is where parallax can appear.

Locking in Parallax Settings

After you have made your adjustments shooting at different distances, some scopes allow you to lock in your changes with your side focus.

Most rifle scopes with medium or high variable power will have a dial for locking in your settings at your typical engagement distance.

Meanwhile, scopes with a fixed parallax have a much wider depth of focus. They cannot lock in, and the trade-off will be more inaccurate shots beyond their built-in parallax-free settings.

Frequently Asked Questions (FAQs)

Here are some of the most frequently asked questions when it comes to solving Parallax.

What Is the Error of Parallax at Close Range?

Within a close range of around 100 yards, the parallax error will not affect accuracy.

The reticle error from the center would be around 1/5th of an inch or barely noticeable. Parallax will only become a major concern once environmental factors affect your bullet’s trajectory.

What Is the Difference Between Fixed-Parallax Scopes and Adjustable-Parallax Scopes?

As the name suggests, fixed-parallax scopes are designed to be parallax-free within a given distance (typically under 100 yards). In contrast, adjustable parallax scopes allow you to adjust for parallax across distances, often to infinity.

If your scope has adjustable parallax, it will come with a side focus adjustment, typically found on the left side of the rifle scope opposite the windage turret.

What If My Scope Doesn’t Have Parallax Adjustment?

Should your scope not have a parallax adjustment feature, it will instead be parallax-free within a specific distance. The scope is designed to not have any parallax issues within this range.

Final Thoughts on Parallax on a Scope

Parallax is a phenomenon (more commonly experienced by long-distance shooters) wherein their crosshairs drift off from where they are trying to aim when using a scope.

Fortunately, you can overcome parallax and ensure true-accuracy shooting by realigning your reticle with a dedicated side focus adjustment knob. You can also make adjustments to your head position to eliminate this issue.