Mr. Spock, We're Inside A Parallax Universe - Brief Article

While you are sighting-in, try checking your scope for parallax. Parallax is the apparent optical displacement of an object in the scope's lens. To check for this phenomena, set up the firearm on bags with the scope pointed at the target at the distance you wish to sight-in.

Without touching the scope, look through it and move your head slowly from side to side and up and down. If you can see any movement of the crosshair on the target, you have a parallax situation.

If you can see a movement of an inch, you will probably never shoot a group of less than 2". It gets much worse than that if your parallax is larger than 1".

Some pistol scopes are set to be parallax free at 100 yards; others at set for 50. Obviously, if you want to give away any accuracy you need to do it at shorter, not longer.

The solution to a parallax problem is to return the scope to the manufacturer for repair and readjustment. Scopes that have a parallax adjustment on the objective end usually have distance markings on them. I seldom see that work out to be correct for the distance marked.

On one particular manufacturer's rifle scopes, I usually find the scope to be parallax free at 100 yards if I adjust it to about the 180 yard distance. If your scope is parallax free at 100 and you check it at 50, you will almost always see an inch or two of movement at that distance.

Fact of life-- optics do not have an infinite adjustment from zero distance to as far as you see.

While you are at it, you might even follow the manufacturer's recommendations on how to adjust the ocular end to suit your eye. That can even make those fuzzy or hard-to-see crosshairs black and crisp.

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