What Do Scope Numbers Mean

Are you looking for a scope? Have fun deciphering the multitude of numbers and dozens of specs you’ll run into on your search. This article will cut through all the confusion and tell you what you need to know about those numbers and what they really mean to you.

Scope specifications help you match the scope to your gun and your particular shooting application, but only if you understand how they will affect what you see and the way you shoot. Read ahead to answer the all-important question.  What do Scope Numbers mean?

This guide will examine the most common numbers and specifications that you will see associated with most long gun scopes. It serves as a glossary of terms with essential explanations. Let’s get started.

Here is a partial list of specifications for the popular Leupold VX-6HD 4-24x52 scope.

scope magnification

Numbers That Affect What You See

A rifle scope is a miniaturized telescope that helps you shoot more accurately. With that in mind let’s start with the obvious magnification and go from there. Scopes come in two types; fixed power scopes (one magnification) and variable power scopes with a magnification range.

Magnification

magnify scope

Magnification means that the image through the scope appears closer than it appears to the human eye (eg. 3x means that the image appears three times closer than it does with the naked eye.)

What it means to you: The above scope has a range of 4x-24x, which is a very wide range. Most hunters will never need more magnification than the classic 3-9 power variable. If you are a long-range hunter or competitor (300 plus yards), consider higher power optics. Bear in mind that a lower power scope may be more suitable than a higher power scope for your application. Target shooting and long range shooting will require a higher power magnification.

Zoom Factor

Zoom factor is the ratio of minimum magnification to maximum magnification in a variable power scope.

rifle scope magnification

What it means to you: The above scope has a zoom factor of 6x (24x / 4x = 6x) a 3-9 scope has a zoom factor of 3x. One might be tempted to go for the biggest zoom factor possible, but that may not be a good choice. Zoom costs money! The 6x scope above costs about $2000. You can score a good 3-9x (3x) scope for less than $300. (Budget scopes with high zoom factors generally have poor images.) For reasons that will become apparent, high magnifications are worse for many hunting situations. Get only the magnification range needed for your application.

Objective Lens Diameter

The diameter of the objective (front light gathering) lens

What it means to you: A larger objective lens will gather more available light. So let’s get a big one right! Not so fast. In a moment, you will learn that many scopes don’t need a large objective lens to produce a good image. Also, large objective lenses may limit your mounting options. The size of the objective lens is just one of many considerations.

Exit Pupil Important But Often Overlooked

Exit Pupil

rifle scope magnification

The diameter of the light beam that leaves the ocular lens when you look through the scope. Exit pupil mm = Objective Lens Diameter mm / magnification.

What it means to you:  The diameter of the human eye pupil (the variable opening in the eye that lets in light) is 2mm to 4mm in daylight and 4mm to 8mm in the dark.

In a hunting situation at dusk, the human eye pupil is 5mm to 6mm in diameter. That means your objective lens diameter only needs to be 5-6 times your magnification at dusk. Inside 250 yards, most shooters will do just fine with their 3-9 adjusted to 7x or lower. 7x times 6mm exit pupil = 42 mm objective. 42mm objective / 9x still gives a respectable 4.7mm exit pupil. The eye does not use any extra light from an exit pupil larger than your eye pupil.

OK, I’ll admit that I have a Vortex 3-12x56mm scope with an illuminated reticle on my 7mm-08 hog gun. But it allows me to make headshots on hogs from a stand 170 yards away at 10x with a 5.6mm exit pupil in really low light.

Check This Video from T.J Schwanky Outdoor Quest TV explaining “Exit Pupil in a Rifle Scope”.

Eye Relief

Eye relief is the distance you must hold your shooting eye from the eyepiece scope lens in order to see the entire image produced by the scope. 

Eye Box

scope sizing

The position of your eye behind a scope that allows for lateral and axial movement on each magnification setting of that specific scope while still maintaining a full field of view.

What it means to you: More is better. Longer eye relief means less chance of “scope bite .” Eye box isn’t that complicated. It’s how much forward/rearward eye relief slack you have and still see a good image. More is better.

Diopter Adjustment (Reticle Focus) And Parallax Adjustment

Parallax Adjustment

rifle scopes explained

A internal lens adjustment that puts the reticle and the target on the same focal plane.

Diopter Adjustment

Magnification adjustment of the rear ocular lens to bring the reticle into sharp focus.

understanding scopes

What it means to you: This is not just about reticle focus. I’m going to kill a few birds with one stone here so consider the following:

  • Scopes are generally designed so that the reticle is in focus at zero ocular adjustment for those with “perfect” far vision.
  • Scopes are generally designed so that a parallax-free image is in sharp focus for those with “perfect” far vision.
  • It is not necessary to shift eye-focus from near to far vision when looking through a scope. Both reticle and target image should be in focus simultaneously (on the same focal plane).
  • If you have far vision glasses (not readers), they should theoretically correct your far vision close to “perfect.”
  • Ocular adjustment is provided because everyone’s vision is a little (or a lot) different.

Reticle focus and parallax adjustment are not designed to take the place of your far vision glasses. Usually, I wear far vision glasses with bi-focal reading lenses. However, I have a pair of  FAR VISION ONLY glasses that I use for scope shooting. I keep some readers in my pocket while I’m in the blind. Take extra care to avoid scope impact with glasses when shooting high recoil scoped rifles. 

Field of View (FOV)

understanding rifle scopes

The size of the area that can be seen while looking through a riflescope. Field of View refers to the area that can be viewed in feet at 100 yards or meters. The field of view is directly related to magnification. At higher scope magnification, the field of view is smaller.

FOV is also given in “angle of view” in degrees. Unless you are a techie, don’t worry about that. Just go with feet at 100 yards.

What it means to you: FOV is dependent on magnification and scope design. More FOV allows you to pick up targets more quickly and see what’s going on around your target. Viewing a wider area helps with moving targets.  More is better, but FOV can affect exit pupil in scope design. Look at both numbers carefully.

Parting Shots On What You See

Scope manufacturers throw around a lot of numbers and terms. Here are some you will run into:

  • Light Transmittance %. The percentage of light that makes it through the scope to your eye. More means a brighter image, but most modern, well-made scopes have very high transmittance. I don’t pay much attention to these numbers.
  • Lens Multi-Coatings. Much more important. The coatings bend different colors so that they all line up for a sharp, crisp, vibrant image. The only way to measure is to look through the scope for yourself. Higher-end scopes produce sharper, more detailed images. However, scope coating technology has come a long way in recent years, and many modestly priced scopes have very good multi-coatings.
  • Scope Tube Diameter. Most tubes are either 1” (25.4mm) or 30mm. Some are larger still.  Larger tubes accommodate bigger lenses. Larger lenses are easier to grind to perfection      and less critical to mount and align. In many cases, this means a better overall image. Larger tubes also allow for lower diffraction angles (less bending) of the light stream. This can result in less distortion, thus improving the scope image.
  • Resolution is a measurement of the riflescope’s ability to distinguish fine detail and produce a sharp image. Better resolution also delivers more intense color. Resolution is determined by the quality of the optical components, the type, and quality of the optical coatings, lens alignment, and other factors. Look through a scope at a distant target to judge for yourself.

Mechanical Adjustments On A Scope: What The Numbers Mean

Elevation And Windage Adjustment Value Per Click

When zeroing a scope, it’s the distance one click will move the point of impact at 100 yards. ¼ MOA= ¼ inch. .1 MIL = about ⅓ inch.

Windage And Elevation Adjustment Range

Total adjustment range before you hit the stops. A larger tube diameter allows for more adjustment range. They are given in MOA or MIL on most scopes. Long-range shooters who dial in hold-over need more elevation range.

Elevation / Windage Adjustment Per Revolution

Per revolution of the turret. Folks who dial in elevation like even numbers to keep up with the number of turns needed.

Reticle Subtensions Or Hash Marks

These marks on the reticle allow for hold over / hold off without dialing in a correction with the turrets. There are dozens of Bullet Drop Reticles (BDC) in use. See the scope manual for details.

scope magnification explained

                                                           Typical MOA Reticle

Winding Up

I hope this article sheds light on scope numbers and what they mean to you. There is a lot to consider when you are going to put down your hard-earned cash for the scope thet lives on top of your favorite rifle.

For the best guides, reviews, and recommendations on all categories of scopes, look no further than Huntingmark.com. Check out the articles from the Huntingmark scopes-optics panel of experts to find a good scope for your needs.

Be safe and shoot often!

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