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The Best

Scope Parallax

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BSA 3-9X40 Sweet 22 Rifle Scope with Side Parallax...
  • Advanced optical rifle scope with quick-change turret system
  • Side parallax adjustment and multi-grain turret
  • Water-, fog-, and shock-proof
  • 40-millimeter lens with camera-quality glass and 3-9X...

Buyer's Guide: Scope Parallax

How to Adjust Parallax?

What exactly is scope Parallax? Scope Parallax is the apparent motion, swimming, or oscillating movement when you look your eye and head in another direction. This often happens when the object in your sight isn't on the same optical axis as your reticle or in focused view. When this happens, a phenomenon called parallax kicks in and your eye can shift left or right by as much as 6 inches at a time. If you've ever been near a rifle at a hunting blind, you know just how important this ability can be.

The key to scope parallax is knowing what causes it. In essence, it's an exaggeration of the effects of eye-focusing and cross-focus adjustments. Eye-focusing adjustments like tilting your head slightly to the left or right, allowing the reticle to open up further, etc. These adjustments naturally make objects appear closer and larger but cause the reticles to over-contribute to the size of things. Over-contribution occurs most commonly with large, fuzzy reticles.

What causes parallax to happen is simple; objects on either or both sides of the erector tube will tend to shift out-of-line with the viewing angle. To explain this in laymen's terms, imagine a baseball in the front yard while you're standing at the base line. Your scope, with a little help from the wind and your eye, appears to be moving toward the right. But because your eye is focusing on the right-hand corner of the baseball, the distant object appears to be slightly farther away. Because of this discrepancy, the object's actual distance from your sight picture becomes more significant than the actual distance the thing is in reality.

As you increase the magnification, the scope will compensate by bringing the reticles closer together and further from the center of the viewing angle. This creates an optical illusion where the objects on either or both sides of the tube are magnified. If you hold the scope at the recommended 100-meter distance, the effect will be even further stretched because the object will be further away from your point of aim. The resulting shots will have increased scatter from each shell hit, leading to a smothering effect on accuracy. In essence, the target will appear as if it is being hit repeatedly.

The best way to correct this problem is to raise the crosshairs on the side of the reticle. Most scopes have a small notch at the top of the crosshair; this will increase the amount of correction needed to make the reticles appear along the bore of the shot. This is done by adjusting the elevation knob to move the crosshair up and down until the wanted effect is achieved.

Scopes with crosshairs can also be adjusted by moving the knobs in different directions. For instance, to get rid of the optical illusion, you can move the adjustment knob in a clockwise direction. In most cases, a right-handed individual will find this helpful since left-handed individuals tend to see everything clockwise. In addition, it is easier for right-handed people to use this adjustment method than left-handed people.

For more accurate shots, you can set the scope at a longer distance than the shortest measurement over the crosshairs. Ideally, this should be at or just slightly more significant than the distance between the top of the front sight and the crown of the scope itself. The rule of thumb is that you should never have to touch the side of the scope to get to the other side. Some manufacturers have made their scopes adjustable using a knuckle, which is an excellent addition to any quality scope. The knuckle adjustment allows you to increase or decrease the amount of windage in the vertical.

To focus the crosshairs on the target, you must first focus the lens itself on the target and then pull the focus lens away from the sight itself. Once the focus lens is focused and in place, you can then concentrate the crosshairs on the target. You want to focus the lens first because it allows for a more stable shot. The parallax will not shift when the focus lens is pulled away from the sight, providing better accuracy as the distance is increased.