Of all the elements of scopes, parallax is one of the most confusing. Most hunters don’t fully understand the concept, even though their expensive scope may have a special adjustment dedicated to it. Should you adjust parallax as the yardage of your shot changes, or is it insignificant enough to ignore?
I was snowed in in South Dakota with hunting partner Joel Harris, marketing and public relations director for Zeiss Sports Optics. While a blizzard howled outside, I finally got the answer to this question in terms I could understand. “Parallax is essentially an optical illusion,” explained Harris. “Parallax presents itself as the apparent movement of the reticle, in relation to the target, when your eye moves off center of the sight picture (exit pupil); in more extreme cases, it appears as an out-of-focus image. It indicates that the scope is either out of focus or, more specifically, the image of the target is not occurring on the same focal plane as the reticle. Maximum parallax occurs when your eye is at the very edge of the sight picture (exit pupil). Even when parallax is adjusted for a designated distance, there is an inadvertent error at other distances. Most brands of scopes that do not have a parallax adjustment are pre-set at the factory to be parallax free at or around 100 yards; rim fire and shotgun scopes are set at or around 50 yards. Most scopes of 11x or more have a parallax adjustment because parallax worsens at higher magnifications. 
“Generally speaking,” Harris continued, “parallax adjustment is not required for hunting situations and is primarily a feature used and desired by target shooters. A 4x hunting scope focused for 150 yards has a maximum error of only 8/10ths of an inch at 500 yards. At short distances, the parallax effect does not affect accuracy. Using the same 4x scope at 100 yards, the maximum error is less than 2/10ths of an inch. It is also good to remember that as long you are sighting straight through the middle of the scope, or close to it, parallax will have virtually no effect on accuracy in a hunting situation.
“This is another way to think of it that perhaps you can relate to. When you’re sitting in the passenger seat of a vehicle, it’s hard to look at the speedometer and tell how fast you are going because your eye, the needle, and the mph number are not all lined up. So to you it looks like you’re going 35 when you’re really going 55. But the person behind the steering wheel has his eye, the needle, and the mph number all lined up straight in the same focal plane, and therefore gets a true reading.” Now I get it.
For more information about Zeiss Sporting Optics go to sportsoptics.zeiss.com.
