Riflescopes: 4 Terms You Should Understand



The perfect kill shot on a white-tailed deer requires a steady hand, quiet stalking and good vision. The first two factors require repetition and a commitment to getting better with experience. The latter can be greatly improved with the right equipment. A type of scope you ultimately choose will come down to the type of firearm it’s attached to, what type of shooting you’ll be doing and of course personal preference.

An old rule of thumb is that you should pay about half the amount for the scope that you paid for the firearm. Red dot sights and scopes are perfect for beginners and veteran hunters alike because unlike iron sights, they lower the error margin significantly when aiming. They also magnify the target, making scopes an excellent addition to any firearm for older hunters or anyone with less than perfect vision.

There are a few details to consider before investing in what will become an important part of all your future hunting experiences.


There are two types of scopes as it pertains to magnification: fixed and variable power. The previous magnifies all images by a set amount, whereas the latter have ranges of magnification power. The numbers tell you the power and the objective lens size.

The Leupold Fixed Power Riflescope, as listed on the Cabela’s website, has either 2.5x or 4x magnification capabilities. The target will thus look two-and-a-half times larger though the scope than with the naked eye, or four times larger with the other option. Variable scopes provide a range of magnification. Thus a 2-4x scope can be adjusted to magnify objects anywhere from twice its size to four times its size.

The last number in the series, for example 3-9×50, tells the diameter of the objective lens. The larger the objective lens, the more light that enters the scope, which in turn produces a clearer image. Most deer are harvested at 25 to 40 yards, so a lower-powered fixed scope is perfect for this purpose. Those plinking prairie dogs and rabbits from 200-plus yards could benefit from a variable, long-range scope.


Simple reticles, also called crosshairs, were one of many invention of 17th century biologist Robert Hooke. Today there are several types of reticles, and the one you choose will depend on where and what you’re hunting, along with personal preference.

Duplex reticles are the most common and universal. These are the typical horizontal and vertical lines that intersect in the center to form the “target.” European-style reticles with the thick outer lines are particularly useful when dealing with shadows.

Mil-Dot reticles were originally developed for Marine snipers. The crosshairs have dots spaced one millimeter apart to help determine the distance an object is from you. A mil means mil-radian, or 1/6283 of a circle. It takes practice to quickly calculate distance based on the number of dots your target is touching through the scope, but gets easier with time. Illuminated and BDC reticles are two more advanced, and more expensive options.


The optical illusion created from the apparent movement of the reticle as it relates to your target is known as parallax. An easier way to describe parallax is looking at the hands on a clock from an angle other than being right in front of it. While the time may actually be 12:10, it may look like 11:55 to you while looking at it from a side view.

High-magnification scopes typically come with adjustable parallax. The more powerful the scope, the more margin for error there is when it comes to accuracy. Lower-powered scopes have error margins small enough that it doesn’t effect accuracy much. These scopes will come with pre-set parallax. Further, as long as the shot is right through the middle of the crosshair, parallax has little to no affect on the end result.

Twilight Factor

The accuracy of a scope in conditions where light is low is its Twilight Factor. This number is calculated by taking the square root of the magnification times the objective lens diameter. For example, a 10×40 scope has a Twilight Factor of 20. The higher the number, the better quality image you’ll get in dim light conditions.

Some veteran hunters question the validity of Twilight Factor and dismiss it as a mere marketing ploy. That’s because a cheap 3-9×50 scope has the same Twilight Factor as a $1000 3-9×50 scope. The quality of glass used in the lenses, and the manufacturer, are much stronger indicators as to how your scope will perform in dark conditions than the Twilight Factor alone.

Once you decide the type of scope you need and want, the best advice is to spend a little more on the next one up the ladder. It’s best to overdue than under-due with scopes, and you’ll thank yourself on your first hunting trip with it.

2 thoughts on “Riflescopes: 4 Terms You Should Understand

  1. “The larger the objective lens, the more light that enters the scope, which in turn produces a clearer image.”

    Nope. Brighter, not clearer (see “twilight factor”). And one of the reasons scope prices tend to climb exponentially with larger lenses is that it’s much more difficult to manufacture large lenses with the precision required to produce a sharp image.

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