Telescopic Sight - Adjustment Controls

Adjustment Controls

A telescopic sight can have several adjustment controls.

• Focusing control at the ocular end of the sight – meant to obtain a sharp picture of the object and reticle.
• Elevation or vertical adjustment control of the reticle.
  • Zero-stop elevation controls can be set to prevent inadvertently dialing the adjustment knob "below" the primary zero (usually 100 meters or 100 yards for long-range scopes), or at least prevent dialing more than a couple adjustment clicks below zero. This feature is also useful on long-range scopes because it allows the shooter to physically verify the elevation knob is dialed all the way down avoiding confusion regarding the elevation status on two- or multi-revolution elevation knobs.
• Windage or horizontal adjustment control of the reticle.
• Magnification control – meant to change the magnification by turning a ring that is generally marked with several magnification power levels.
• Illumination adjustment control of the reticule – meant to regulate the brightness level of the lit parts of the reticles crosshairs.
• Parallax compensation control.

Most contemporary telescopic sights offer the first three adjustment controls. The other three are found on telescopic sights that offer a variable magnification, an illuminated reticle and/or parallax compensation. A rather common problem with the elevation and windage adjustment controls is that once smooth working adjustment turrets 'get stuck' over the years. This is generally caused by long term lack of movement in the lubricated turret mechanisms.

Older telescopic sights often did not offer windage and elevation adjustments in the scope, but rather used adjustable mounts to provide adjustment. Some modern mounts also allow for adjustment, but it is generally intended to supplement the scope adjustments. For example, some situations require fairly extreme elevation adjustments, such as very short range shooting common with airguns, or very long range shooting, where the bullet drop becomes very significant. Also, loose manufacturing tolerances may result in base mounting holes being less than perfectly aligned with the bore. In this case, rather than adjusting the scope to the extremes of its elevation adjustment, the scope mount can be adjusted. This allows the scope to operate near the center of its adjustment range, which puts less stress on the internals. Some companies offer adjustable bases, while others offer tapered bases with a given amount of elevation built in (commonly listed in MOA). The adjustable bases are more flexible, but the fixed bases are far more durable, as adjustable bases may loosen and shift under recoil. Also, adjustable bases are considerably more expensive, as well.