What Is Parallax on a Rifle Scope (and How to Adjust It)
You are stretched out behind the rifle at 300 yards, and as you settle your cheek the reticle seems to drift across the target — move your head a little, and the crosshair slides off the bullseye. That drift is parallax, and at distance it quietly opens up your groups. Parallax is the apparent movement between your reticle and the target when your eye shifts behind the scope, and it happens because the target's image and the reticle are sitting on slightly different optical planes — you remove it by focusing the reticle, then dialing the scope's parallax adjustment until the reticle stops moving.
Key takeaways
- Parallax is the reticle appearing to move against the target as your eye moves, caused by the target image and the reticle not being on the same focal plane.
- It is usually negligible inside about 150 yards but can shift your point of impact noticeably at longer range and higher magnification.
- You correct it in two stages: first focus the reticle with the eyepiece ring, then turn the side-focus or adjustable-objective dial until the reticle stays still when you move your head.
- Not every scope adjusts for it — many are fixed at one distance, while precision scopes like the Accufire EVRO-12 and ATRO-20 use a side-focus that dials from 50 yards to infinity.
What parallax actually is
Inside a scope, the target's image is projected onto a plane and the reticle sits on its own plane. When those two planes line up perfectly, the reticle stays glued to your aim point no matter where your eye is behind the eyepiece. When they do not line up, moving your eye makes the reticle appear to shift across the target — the same effect you see when a car's speedometer needle reads differently from the driver's seat versus the passenger's. It is not the rifle moving; it is your line of sight crossing two mismatched planes.
When parallax matters
For most shooting inside roughly 150 yards, parallax error is small enough to ignore, which is why many general-purpose and lower-power optics simply fix it at one distance. As range and magnification climb, the picture changes: a tiny reticle shift that was harmless up close now represents inches at the target, and a precision shot you thought you held can land off call. If you shoot past a couple hundred yards or run high magnification, an adjustable parallax system earns its place.
How to adjust parallax, step by step
Work in order. First, focus the reticle: point the scope at a plain, bright background several yards away and turn the eyepiece (ocular) ring until the reticle itself looks crisp — this sets the scope to your eye and is done once. Next, set the parallax dial to the rough distance of your target. Finally, fine-tune by observing head movement: keep the reticle on the target and shift your head slightly up, down, and sideways. If the reticle slides off the aim point, turn the parallax dial in small increments until the reticle stays locked in place as your head moves. When it no longer drifts, parallax is gone for that distance.
Fixed, adjustable-objective, and side-focus systems
Scopes handle parallax three ways. Fixed-parallax scopes are preset at the factory — often around 100 yards, or closer on rimfire optics — and cannot be changed, which is perfectly fine within their intended range. Adjustable-objective (AO) scopes let you rotate the front bell to focus parallax out. Side-focus scopes move the control to a third turret on the left of the tube, marked in yardage, so you can adjust without reaching forward. Accufire's variable scopes use side focus: both the EVRO-12 and the ATRO-20 dial parallax from 50 yards out to infinity.
| Parallax system | How you adjust it | Typically found on |
|---|---|---|
| Fixed | No adjustment — preset at one distance (often ~100 yd) | Lower-power optics, many red dots and LPVOs |
| Adjustable objective (AO) | Rotate the front objective bell | Older and dedicated target scopes |
| Side focus | A left-side turret marked in yardage | Modern precision scopes (Accufire EVRO-12, ATRO-20: 50 yd–∞) |
An honest note on what it can and cannot fix
Dialing out parallax sharpens your point of aim, but it does not correct a poor zero, a loose mount, or inconsistent shooting position. If your groups wander, parallax is one suspect among several — check that the reticle focus and the parallax setting agree first, then rule out mechanics. And on a fixed-parallax optic, there is nothing to "fix": it is optimized for a set range, so just keep your expectations matched to that distance rather than chasing an adjustment that is not there.
Shooting far enough that parallax matters? Accufire's variable scopes put a yardage-marked side-focus dial within reach for a clean sight picture at distance — explore Accufire rifle scopes.
Accufire ATRO-20 Advanced Tactical Rifle Scope — $649.25. A 2.5–20x50 first focal plane optic with side-focus parallax from 50 yards to infinity, 3.22–3.5 in of eye relief, and a 30 mm tube. View the ATRO-20.
Frequently asked questions
What is parallax on a rifle scope?
Parallax is the apparent movement between the reticle and the target when your eye shifts behind the scope, caused by the target image and the reticle sitting on slightly different focal planes. At distance it can move your point of impact.
At what distance does parallax matter?
Parallax is usually negligible inside about 150 yards. It becomes significant at longer range and higher magnification, where a small shift of the reticle represents inches at the target and can pull a precise shot off call.
How do you adjust parallax?
First focus the reticle with the eyepiece ring against a plain background, then turn the side-focus or adjustable-objective dial until the reticle stays still against the target when you move your head slightly. When the reticle stops drifting, parallax is corrected for that distance.
Do all scopes have parallax adjustment?
No. Many lower-power optics and red dots have fixed parallax preset at one distance, while precision scopes add an adjustable objective or a side-focus dial. The Accufire EVRO-12 and ATRO-20 use a side-focus that adjusts from 50 yards to infinity.
Is parallax the same thing as focus?
They are related but not identical. Focusing the reticle with the eyepiece and focusing the target with the parallax dial must agree so both land on the same plane, and it is that agreement, not focus alone, that removes parallax.
Parallax is one of several scope fundamentals worth understanding before you dial for a shot. If you are still learning the controls, our guides to how to zero a rifle scope and reading rifle scope numbers cover the basics that parallax builds on.