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NAVIGATION
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Parallax Error and Adjustable Objective Riflescopes
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PARALLAX ERROR - Parallax error is when changing positions of your eye will change the point of aim of your scope. The error is related to the distance the target is from you. Most sporting rifle scopes are set to be Parallax Error-Free at 100 yards. That is, when aiming through your scope at a target 100 yards away, the point of aim stays the same regardless of the position or movement of your eye (side to side or up/down).
TEST FOR PARALLAX ERROR - It’s pretty simple (and enlightening!) to test your scope for parallax error. Position your scope or scoped firearm in sand-bags so that it is aiming at a 100 yard target. Now, without touching the gun or the scope, move your head from side to side while looking through the scope. If the crosshair moves around on the target, you’re seeing parallax error at that distance. How much error depends on how much movement. I’ve seen some scopes where the movement was 4-6inches! To find the distance where your scope is parallax error-free, do this experiment at 25, 50, 75, 100, and 125 yards. The distance where it is error free will also be the distance at which you shoot most accurately.
PARALLAX ADJUSTABLE SCOPES -
Scopes with an adjustable objective (AO) allow you to set the distance at which they are parallax error-free. These scopes are also designated as Parallax Adjustable (PA), Side Focusing (SF), etc. It's misleading to call this feature "focusing" because its really parallax correction. Its also important to note that the distance markings on the parallax adjustment are quite often not exact. This is partly due to the scope user's own eye optics, but also due to changes within the scope from one magnification setting to the next. In fact, some high end scope companies have addressed this by not putting specific distances on the parallax adjustment. Instead, they say use the test (above) to find the point of zero parallax error for each distance yourself. Use a silver or white paint pen to mark the positions. When all other features are equal, adjustable parallax can make a cheap scope a bargain by simply being able to exactly dial out all of the parallax error when aiming.
HOW CRITICAL IS PARALLAX? - For pinpoint aiming purposes, parallax error is most critical at under 100 yard distances. Rimfire and air rifles absolutely need adjustable parallax due to shooting under 100 yds. On the other hand, big game scopes are set to be parallax error free at 100 yards. At under 100 yards, BIG game are large enough that parallax won’t throw you too far off your aiming point. And beyond 100 yards, the error is simply less for the difference in distance. Adjustable Parallax scopes have a lot of adjustment under 100 yards but just a little as range increases over 100 yards. So, if your scope tests parallax error-free at 100 yards, it is going to work just fine for most big game hunting situations. But, if it shows a lot of parallax error at 100 yards, it is simply not going to shoot accurately and reliably. And, if you're hunting SMALL game at distances over 100 yards (ie. varmints and prairie dogs) the ability to dial out parallax error becomes a necessity. |
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©2005DARC
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