What the numbers on a scope mean

It is logical that the first time you decide to buy a optic sight or scope, you ask yourself what 3-9 × 40 means in a optic sight , or in any optics in general. What are these measurements? It seems like a Chinese thing, right?

Don’t worry, in this article we are going to explain in the simplest way, what those numbers mean and why they should interest you if you are thinking of choosing your next sight. We are going to use a 4 × 32 and a 3-9 × 40 scope as an example , but what you will learn here can be applied to any other scope such as a 4 × 20 or 2-7 × 32, etc.


Meaning of the numbers in a optic sight

First things first, let’s separate the numbers to better understand each part of them. Let’s take the following 2 sights / scopes as an example:

  • Look 1: 4 × 32
  • Look 2: 3-9 × 40

Magnification or Zoom

You will observe that always in the numbers of the sights there is an “x” that divides them.

That said, the part to the left of the “x” in our example:

  • Look 1: 4
  • Look 2: 3-9

It refers to the scope’s magnification or zoom ability and would read as follows:

“ Sight 1 has a magnification or zoom power of 4 times. “This means that, if you were to observe a target with your normal visual ability, and then use that scope to observe the same point from the same position, the target would have been magnified 4 times (its image would look larger).

When is a optic sight fixed and when is it adjustable?

Now you ask yourself, what happens in the case of sight 2? Very easy.

When on the left side of the “x” there are 2 numbers separated by a middle dash (-), this means that the zoom of our sight is adjustable. And it is given as follows:

” The zoom of the scope 2 is adjustable from 3 to 9. ” The minimum magnification power being the number to the left of the middle dash (in our example 3) and the maximum zooming power the number to the right of the middle dash ( in our example 9).

It is worth mentioning that there will be intermediate points between 3 and 9 that we can select (4, 5, 6, 7, 8) to regulate and better focus on the objective depending on the distance at which we are.

In our example then:

  • Sight 1: 4 × 32 (4x fixed sight)
  • Sight 2: 3-9 × 40 (Sight adjustable from 3 to 9 times)

Objective lens diameter

Now that we understand what the numbers to the left of the “x” mean, we only have to know what the number to the right of it means. Simple.

The numbers to the right of the “x” refer to the diameter in millimeters of the objective or front lens of our optic sight. In our example:

  • Look 1:32 (32mm diameter front lens).
  • Look 2: 40 (front lens 40 millimeters in diameter).

In other words, it is the size of our front lens. Now, you ask yourself, and how does this influence?

Why is the size of the objective lens of our sight important?

As a general rule, the larger the size of our front lens, the greater the field or spectrum of vision and the greater the light that enters the scope and , therefore, it will allow you to see more and better. This is especially important when the light is poor (sunrise and sunset).

This has its pros and cons. The biggest advantage is undoubtedly the greater amount of light, but a disadvantage is the increased weight in the scope, which increases the weight of the rifle in general and therefore makes freehand shots more difficult.

How to read the numbers on a optic sight or scope

Finally, let’s see how our 2 examples would fully read:

  • Sight 1: 4 × 32 (Fixed sight 4x by 32 millimeters in diameter on your front lens).
  • Sight 2: 3-9 × 40 (Sight adjustable from 3 to 9 magnification by 40 millimeters in diameter on its front lens).

It should be noted that this reading criterion is applicable to any type of fixed or variable zoom optics, whether they are optic sights, binoculars or telescopes.

Scope of optic sights

Sometimes we are asked: How far does a 4 × 32 scope have? Technically there is no such thing as scope in sights or binoculars because they are magnifying elements. What they basically do is make an object look closer than it actually is. What you should do is guide yourself from the magnification or zoom to decide.

Will a 4 × 20 scope allow me to see a deer at 200 meters? The answer is yes, but the big question is how big or how close do you want to see that deer? The same philosophy applies to a 4 × 32 or a 3-9 × 40 and whatever other magnification you have.

For example: Suppose that with your eyes you see an element in the distance and you put a ruler next to your eye to measure its height, and it is 2 centimeters. If now, from the same position, you see the same element with an X2 magnification or zoom scope, you are going to see that same element larger, how much larger? 2 times larger (4 centimeters).

In this way, when choosing a sight you must ask yourself: What do you want to see? and how much bigger do you need to see it?

What is the range of a 4 × 20 scope?

A 4 × 20 viewfinder is recommended for distances between 50 and 100 meters.

What is the range of a 4 × 32 scope?

A 4 × 20 viewfinder is recommended for distances between 50 and 100 meters.

What is the range of a 3-9 × 40 scope?

A 3-9 × 40 viewfinder is recommended for distances between 150 and 250 meters.

What viewer do you recommend me to buy

Start with something cheap but that allows you to climb. 3-9 × 40 scopes , as we saw, can serve a myriad of purposes, both for precision shooting and hunting. Start with that and then think of something higher magnification. I leave you my recommendations below.

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