It seems one of the most profoundly misunderstood concepts in shooting is Parallax.
“Parallax is an apparent displacement or difference in the apparent position of an object viewed along two different lines of sight.”
The definition doesn’t seem to help clarify the situation either. For our purposes in shooting a scoped rifle, we encounter Parallax when our target and our reticle are on different focal plains. Just like shooting a gun with iron sights, our eye can only focus on one plain. We can focus on the target, the front sight, or the rear sight, but not all three at once. (For best results, focus on the front sight) When we look through a rifle scope, sometimes we have to choose which to focus on, the target or the reticle. If you have to pick one or the other, your scope is out of proper adjustment for your shot. When this happens, a movement of the position of the shooter’s eye makes it appear that the reticle moves against the target. The result is a less accurate shot placement. When we focus the Target and the Reticle together, movement of the eye doesn’t effect the apparent position of the reticle, thus a more precise shot placement can be made.
Some scope makers claim that Parallax is a distortion because of inferior optics (of their competitors) but the truth is that no matter how good of a glass they have, Parallax is indeed there. We see it most often come into play when scopes are set to power levels above 9 to 12 in most optics. However we can not eliminate it at every power setting, at every range. That has proven to be either virtually or practically impossible.
So Parallax needs to be focused and we generally have it in one of a couple ways. First, is internally, preset at the factory. Usually this is set at 150 yards in centerfire rifles of 3-9 (or some 4-12) power, or 100 yards on fixed powers. Rimfire scopes tend to be set at 45 to 50 yards. Scopes that come with power adjustments greater than 3-9 often come with an Adjustable Parallax. Most common is on the Objective Bell of the scope. Gaining popularity is the side parallax turret. Personally I like the new side turret types best as they are the most convenient for the shooter to use. How you use them is simple. You set the turret, or the bell ring, to the indicated range of your target and that’s about it. Most scopes, if they have done their part, that’s all you need to do. Some scopes, you have to play with that adjustment a little to find the actual position for a focused parallax. Some guys call this a “Poor Man’s Rangefinder” and sometimes it works, but don’t trust it. There are Rangefinders that use parallax, but they use two objectives instead of just one.
So, I hope we are clear as mud on Parallax now. Thanks for time to read this.
Oh, what? Parallax Free optics? Yes, those are mostly Red Dot types that don’t have any magnification or only have a little. With these, when they are mounted on a weapon, regardless of the eye’s position, if the dot is on the target, the gun is aimed at target and you will hit it.