Parallax Adjustment – 2021 Guide on Understanding and Correcting Parallax

| Last Updated: March 12, 2021

Parallax is a very subtle factor that often goes beyond the head of most newbie shooters unless they experience it in a real life situation.

Considered mostly a matter of concern for pro shooters.

This discussion will open up the topic of parallax adjustment on a rifle scope, and how does it impact the overall shooting performance. 

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What is Parallax on a Scope? 

In the most layman terms, parallax refers to the non-alignment of your eye with the reticle and the target. So when you move your head around when looking through the scope. You find that the crosshairs do not stay on the exact spot and fiddle a little. Parallax can also be a result of the image not being in focus.

Many scopes with variable magnifications offer a parallax adjustment feature in the form of a knob or ring mounted on the scope. Parallax is an important factor when shooting long range because it can impact accuracy and also precision with follow-up shots. 

More on this later.

Parallax Adjustment Terminology and Common Concepts

Before diving deeper into the concept of parallax adjustment. Let’s take a look at some common terminologies related to the topic.

Reticle

Otherwise known as crosshairs in simpler terms. A reticle is the image of lines and dots you see when viewing through a scope on a blank plain spot. Reticles come in different types and can range from simple crossed lines to more deliberate tactical designs. 

Parallax Error

As already evident from the name, parallax error refers to the shift in the point of aim of the reticle. This is experienced when the scope-to-eye alignment is not right. 

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Focal Plane (FFP and SFP)

Focal plane refers to the plane through a focal point and perpendicular to the axis of a lens. In even simpler terms, the focal plane is the plane passing between the lens and the perfect point of focus in an image. 

Scopes come in two configurations: First Focal Plane (FFP) or Second Focal Plane (SFP). 

SFP scopes are more common and cheaper. In these scopes, the size of the reticle stays the same when you increase the magnification. WIth these scopes, you have to calibrate the settings at each magnification point. 

FFP scopes are more advanced and hence more expensive. In these scopes, the size of the reticle changes with the magnification. Hence you do not have to dial the settings everytime you change the zoom. These are mostly preferred by snipers and competitive shooters. 

Objective Lens

The front lens of the scope through which light enters. Bigger objective lenses deliver better clarity and brightness. 

Side Focus

It refers to the small knob that is mounted on the side of the scope tube and is used for adjusting parallax. 

Adjustable Objective

This is another mechanism of parallax adjustment where a ring mounted on the objective lens housing can be rotated to set parallax. 

Diopter Adjustment

Also known as fast focus eyepiece. Diopter adjustment is used to bring the image of the reticle in focus. 

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Why Do You Need to Adjust Your Scope Parallax?

Parallax causes your reticle to appear moving on the target. While it has more to do with the positioning of your head than setting the exact point of impact. Adjusting the parallax of your scope gives you confidence and surety that your shots are going to land on the exact spot where you want. 

Keeping your head stable is very difficult when looking through the scope. This does not only refer to the small blinks and mushy movements of the head or the eye. But the small disturbances that occur while handling different rifle chores. Like charging the bolt, moving to a new target or setting the windage and elevation knobs. 

Parallax adjustment is also required when you switch magnifications. That’s because changing zoom means the lenses have to move. Which also affects the parallax setting. 

Do’s and Don'ts of Parallax Adjustment

Rather than fiddling with the parallax knob on your scope. Keep in mind some best practices and refrains when adjusting the parallax on your scope. 

Let’s check the Do’s first. 

Check the Diopter Adjustment

Since the reticle is the most important and first aiming point inside the scope. You should ensure that your reticle is absolutely clear. Play around with the diopter adjustment when you first use a scope. 

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Diopter settings are individual for each user and should be calibrated when using a new scope

Always Check Parallax When Changing Magnification

Parallax settings start to differ with changing magnification. That’s because the distance between the lenses changes and hence the focal plane. When working at high magnifications (above 4x), always set the parallax when you change the magnification.


Remember the Adjustment Marking for Quick Reference

The side focus knob used for parallax adjustment will have markings for distance. You can start remembering the relevant magnification and turret values at different settings for quick dialing. 

Consistent Head Placement

Parallax is all about eye placement. So make sure you have a comfortable and properly positioned cheek weld. If you need an adjustable stock or cheek riser. Definitely go for it. 

Now let’s check some don’ts.

Never Adjust the Parallax Knob from its Current Position

To get the perfect reading, you have to dial the side focus all the way up until it stops. From here you can dial down to the distance you want. This delivers the most accurate resolution for cant error. 

Don’t Guess With Parallax

Don't rely upon improvised parallax adjustments for ultra long shots. Or when shooting more than the pre-set parallax range for a fixed magnification scope. 

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How to Adjust Your Scope Parallax

Adjusting the parallax on a scope is very easy. Take a look at the step by step procedure for that below:

  1. The first step is to ensure that the rifle’s safety is on.

  2. Before you start adjusting parallax, ensure to set the diopter at the right value.

  3. Aim the scope at a clear background (like a plain wall or the sky) and adjust the diopter knob (located near your eye at the scope) unless the reticle gets absolutely clear.

  4. Once the reticle is clear, you can rest assured about getting the perfect adjustment.

  5. Now aim at the reticle at your target and dial the magnification so the target is clear.

  6. While looking through the scope, move your eye around a bit to check for parallax.

  7. Now dial the parallax adjustment knob/ring all the way out to infinity and then gradually dial it to lower range settings until you get the perfect parallax setting.

  8. Objective rings are more crisp than side knobs which are known to be a bit mushy. So dial according to your setup.

For more detailed instructions on this process, check out this video. 

Conclusion 

Parallax refers to the non-alignment of the reticle and the target in the same plane. This can be easily corrected with the adjustment knob/ring on your scope. Parallax is a major concern for long range shooting (400+ yards) and situations where absolute precision is instrumental. This is generally not a problem for centerfire rifles working on a short to medium range.

People Also Ask

Check out this concise and to-the-point FAQ section that covers the most common doubts about parallax adjustment. 

Does Parallax Affect Accuracy?

Parallax is a crucial factor in determining accuracy when a shot is being made at 400 yards or more. Since that’s the distance where parallax comes into play. Parallax adjustment is essential for precision shooting applications where a difference of just a couple of inches matters. 

Do Fixed Power Scopes Have Parallax?

Fixed power scopes come with a factory-set parallax at a certain range. Generally 50 or 100 yards. However, fixed scopes generally work on low magnifications and parallax is not a big deterrent there. 

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What Does 100 Yard Parallax Mean?

A 100 yard parallax means that when you are aiming at a target exactly 100 yards away through the scope. The image will be parallax free. 

Does Parallax Change With Magnification?

Yes. Parallax changes with magnification and you have to set it every time you make significant zoom changes. More magnification has more chances of parallax error. Whereas, parallax error is less of a problem at low magnification settings. 

Does It Matter If The Scope is First Focal Plane vs Second Focal Plane?

As far as parallax is concerned, it doesn’t matter. But as far as usability is concerned, FFP scopes are better for tactical applications and quick adaptations for follow up shots at long range because the size of the reticle changes with the zoom. Hence, calibrations stay true.



Ankit Kumar is an engineer turned writer who specializes in topics related to firearms, gun safety and weapon tech. His passion towards enrolling in the Army drifted his interest towards light and heavy firearms. He’s a qualified competitive air rifle shooter and an avid nature lover. His other areas of expertise include survival, prepping and firearms/ammo storage. When he’s not writing, he’s either learning a new skill, trekking or enjoying a long drive.