Adjusting Your Scope's Parallax
Parallax...hmm, just what is it? And how do I fix it for my scope?
Unfortunately, many folks mount a centerfire scope on their airgun and fail to realize that the parallax for that type of scope is normally set at 100 yards or even further. Now, translate the actual range you are likely to be shooting with your airgun, and the problem becomes a little more evident.
For a quickie definition of parallax, complete with a simple demonstration, look at the following links:
http://en.wikipedia.org/wiki/Parallax
http://www.arld1.com/parallax.html
The first link defines it, the second link narrows in on the effects of parallax through a rifle scope.
I've cut and pasted some additional explanations of parallax for you in this next section. It will hopefully explain parallax to you in a way that makes better sense than my humble attempt at explaining parallax!
********
********
Parallax problems result from the image from the objective not being coincident with the reticle. If the image is not coplanar with the reticle (that is the image of the objective is either in front of or behind the reticle), then putting your eye at different points behind the ocular causes the reticle crosshairs to appear to be at different points on the target. This optical effect causes parallax induced aiming errors that can make a telescopic sight user miss a small target at a distance for which the telescopic sight was not parallax adjusted.
To eliminate parallax induced aiming errors, telescopic sights can be equipped with a parallax compensation mechanism which basically consists of a movable optical element that enables the optical system to project the picture of objects at varying distances and the reticle crosshairs pictures together in exactly the same optical plane. There are two main methods to achieve this.
- By making the objective lens of the telescopic sight adjustable so the telescopic sight can compensate parallax errors. These models are often called AO or A/O models, for adjustable objective.
- By making an internal lens in the internal optical groups mounted somewhere in front of the reticle plane adjustable so the telescopic sight can compensate parallax errors. This method is technically more complicated to build, but generally more liked by parallax adjustable telescopic sight users—unlike AO models, which are read from the top, the sidewheel's setting can be read with minimal movement of the head. These models are often called side focus or sidewheel models[7].
Most telescopic sights lack parallax compensation because they can perform very acceptably without this refinement. Telescopic sights manufacturers adjust these scopes at a distance that best suits their intended usage. Typical standard factory parallax adjustment distances for hunting telescopic sights are 100 yd or 100 m to make them suited for hunting shots that rarely exceed 300 yd/m. Some target and military style telescopic sights without parallax compensation may be adjusted to be parallax free at ranges up to 300 yd/m to make them better suited for aiming at longer ranges[8]. Scopes for rimfires, shotguns, and muzzleloaders will have shorter parallax settings, commonly 50 yd/m[9] for rimfire scopes and 100 yd/m[10] for shotguns and muzzleloaders. Scopes for airguns are very often found with adjustable parallax, usually in the form of an adjustable objective, or AO. These may adjust down as far as 3 yards (2.74 m)[11].
**********
**********
Ray and Hans Apelles from the "A Team" shoot for and represent Crosman at FT shoots and competitions. They have some very good free information that will help you, the shooter, figure out and fix the annoying little issues that come from using scopes, air guns, different pellets.....they simply have a wealth of knowledge and freely share it with the rest of us as a contribution to the airgunning sport. Granted, the information is for powerful scopes of 18x or higher, but for competition shooters and others who want to enter the field of competition, this is a useful tool.
Check out the following link for assistance in fixing the parallax, or even determining if you have a parallax issue, with your scope.
http://ateam.100free.com/ateamh/A_Team_Parallax_adj.htm
We'll be reviewing some new guns in the next few weeks and hope to offer you a review or two to help you in your buying decisions. Thanks for dropping in and reading along with us!
