Understanding The Basic Components of a Rifle Scope
Rifle scopes may seem like simple tubes with lenses on the both ends and several adjustment controls on the surface. However, these devices are manufactured with many intricately arranged parts. These components work together to magnify an image and place an observer’s eyes on the same optic plane as the target.
Although most scopes differ slightly in design, they all have several similar parts. This tutorial looks at the internal and external structure of a basic rifle scope to help you understand the device and its capabilities.
√ External Components
- Main body – The main body of a rifle scope takes the shape of a tube. In reality, there are two tubes, one placed inside the other. The outer tube protects internal components of the scope, provides the surface area required to mount the scope on a rifle, and holds adjustment controls. The inner tube houses lenses and other internal components of the scope.
- Objective bell – Fixed at the furthest end from an observer’s eye is the objective bell. This is the piece holding a scope’s objective lens. The objective bell is the light collecting apparatus of a rifle scope.
- Eye bell – The eye bell is the end from which you look into a scope. It houses the eyepiece, which helps to determine the furthest distance from which your eye can be positioned and still get a full view when looking into the ocular lens. Located at the eye bell also is the ocular lens, which works together with other lenses to establish the final image.
- Turret knobs – A turret is one of two knobs, which usually protrudes from the middle section of a scope. These knobs adjust windage and elevation settings of the reticle. The reticle or crosshair is usually a ‘+’ sign marker superimposed on the target. It indicates the point of impact when a shooter hits the target. The windage turret is usually located on the side of the tube. By adjusting it, this allows you to move the reticle and correct the aiming point in the horizontal plane (that is left-to-right or side-to-side). The elevation turret, often located on the top side of the scope, moves the reticle up and down or corrects the point of impact on the vertical plane. Turret adjustments may be increased or decreased in a 1/4 or 1/8 MOA (Minute of Angle).
- Power ring – The power ring is a dial usually found on or slightly in front of the eye bell of variable rifle scopes. This part simply adjusts the power or magnification of your scope.
- Parallax knob – Some scopes have a parallax knob. As the name implies, this control helps to correct parallax error to a predetermined distance until a clear picture of the reticle is achieved. This setting prevents the apparent movement of the reticle and the target when you move your eyes away from the center of the rifle scope. Rifle scopes that do not have a parallax knob may have an adjustable objective (AO) instead. This adjustment is essentially a dial located at the objective bell. When correcting parallax error, you will turn the AO dial to focus the objective lens.
- Diopter – This is an additional adjustment at the ocular end of the scope. It rotates the ocular lens so that the observer can focus the reticle on the target. The diopter also matches your viewing condition depending on whether you are short or long-sighted.
√ Internal Components
The internal structure of a rifle scope mostly houses lenses. From the eyepiece to the rear end of the scope, you have the ocular, magnification, focus and objective lenses. Lenses may be coated to reduce light loss and glare caused by reflection.
As such, you will often hear rifle scope manufacturers describing their lenses as coated, fully coated, multi-coated, or fully multi-coated. Coated lenses enhance the light gathering abilities of a scope, especially in low light shooting conditions.
The internal structure of a rifle scope may look a bit complicated, but it can be broken down into three major sections as explained below.
- Objective lens assembly – The larger its diameter, the more light your scope will transmit to the eye.
- Focus lens assembly – A focus lens is responsible for correcting parallax error. With fixed focus scopes, it is set to a parallax-free factory setting at a specified range, usually 100 yards. Scopes that have a parallax knob move the focus lens toward and away from the objective lens.
- Erector tube –The erector tube assembly holds the magnifying lenses and reticle components. When turning the power ring on a variable power scope, the magnifying lenses move within erector tube to adjust magnification power. The reticle may be placed in front or behind the magnifying lenses depending on the manufacturer’s assembly. The former assembly is called a first focal plane (FFP) reticle, while the latter arrangement is known as a second focal plane (SFP) reticle. With FFP reticles, the cross hairs remain the same size as the target. In scopes that have SFP reticles, the cross hairs become larger or smaller as magnification on the target changes. There are many types of reticles. For instance, some may be simple cross hairs or three post arrangements. Other reticle assemblies come with some illumination feature or have a calibrated system with dots or harsh marks.
This guide is just a simple tutorial on the basic anatomy of a rifle scope. It should by no means replace the instruction manual provided by your manufacturer. However, it can help you with some useful information when shopping for rifle scopes. Keep in mind that the ideal scope for you will depend on your shooting conditions, type of gun you use and personal preferences for features like reticle type and color.