Problems With High Power Shooting Scopes

Parallax

• Parallax error is a phenomenon usually encountered when viewing long range targets at high magnification settings. Parallax is an optical illusion of false target movement caused by a shift in the shooter's line of sight down the tube of the scope. The perceived movement is actually the shift in view of the reticles and, since your brain perceives the reticles as fixed, the movement is interpreted as target movement. Most high-powered scopes allow you to calibrate the reticles for the range of your target with an adjustment on the objective bell or with a dial located on the left side of the scope.

Field of Vision

• The field of vision is the horizontal distance viewable through your scope. As a general rule, scopes set on low magnification settings have a greater field of vision and, as the magnification is increased, the field of vision diminishes. An advantage of a large field of vision is that you can use your scope to identify your target before aiming; a small field of vision makes initial identification of your target much more difficult. This shortcoming can be overcome by spotting your target at a lower magnification setting and increasing magnification while maintaining the target centered in your reticles.

Eye Relief

• Eye relief is the distance between the end of the ocular lens and your eye, required for a clear sight picture. The shortest eye relief distance of a scope is at its highest magnification setting. This can become an issue particularly if your scope is mounted on a high velocity rifle that produces heavy recoil when fired. When choosing a high-power scope, make sure that the eye relief, at the higher settings, is sufficient to provide you a safe eye relief distance that will prevent you from being hit by your own scope.

Exit Pupil Size

• The scope exit pupil is the end of the tube that delivers the sight picture to your eye. As the magnification power becomes greater, the size of the exit pupil becomes smaller, possibly to the point of degrading the imagery. This problem is prevalent on scopes with particularly high magnification settings. Fortunately, the majority of scopes operate within magnification settings that allow for sufficient exit pupil sizing.