What Do All The Numbers Mean on Spotting Scopes?

what do the numbers mean on a spotting scope

Once you’ve decided to take your bird watching to the next level and get yourself a good spotting scope, there are a lot of things that you you’ll need to know.

But, even when you know what to look for, the whole business can still be quite confusing.

All those numbers…. What do they even mean?!

To be fair, all of these confusing numbers on a spotting scope are really easy to understand. So, let’s see how.

What Do the Numbers Mean on Spotting Scopes

Explaining the numbers on a spotting scope is very simple once you look at an actual example. So, let’s take this one:

20 – 60 x 80 mm

First, let’s take a look at this pair of numbers on the left side: 20 – 60.

The first number – 20, represents the minimum magnification that you are getting with this scope. That means that the objects observed through this scope will appear 20 times bigger than they actually are in nature.

The second number – 60, represents the maximum magnification that you can get with the scope. Same as before, if you are looking through your spotting scope at 60 times magnification, objects will appear 60 times larger than in real life.

Since there is a hyphen between these two numbers, it means that the magnification can range from 20 to 60. Therefore, you can safely conclude that this is a spotting scope with a zoom.

Now, the number on the right – 80, represents the diameter of the objective lens shown in millimeters.

Remember, the numbers on the left side on an x always represent the magnification power of a spotting scope, and numbers on the right side of the x show the size of the objective lens in millimeters.

This is something that you will most usually see. However, don’t get confused or nervous if the numbers do not look exactly like this.

Let’s take a look at another example:

4 x 32

Even though this one looks a little bit different from the previous set of numbers, it is just the same.

The number on the left side of the x represents the magnification power of 4 on this scope, and the number on the right side of the x means 32 millimeter objective lens.

Even though there is no “mm” written, the number on the right side always represents the objective lens in millimeters.

Moreover, from the numbers given, we can conclude that this is a fixed scope – there is only one number on the left side, which represents the magnification.

One more possibility is this:

5 x scope

This is just the magnification power of a scope written in short. Naturally, it means that the picture you are looking at appears 5 times bigger than what they really are.

Size of Objective Lens

Now, we had two examples that mentioned objective lens: 80 mm and 32. Now you know what this number is, but what does it actually mean?

The larger the number, the larger the objective lens. And larger the objective lens, the more light will the scope let in. More light means that you will get a brighter image and you will be able to see nice details more easily. Moreover, bird watching in conditions with low light will be much more enjoyable. Especially if you like to do this activity at dusk or dawn.

Spotting scopes, in general, have bigger lenses than binoculars. Spotting scopes have greater objective lens diameters because they need to let the light in. If they don’t allow that much light, you would not be able to see a clear and bright picture at high magnification, like 60 x or 80 x.

Here’s a few additional tips from Paul Kennel of Vortex Optics on spotting scopes, enjoy!

Other Numbers

These were the main numbers and those that you will first spot when looking at specifications of a single spotting scope.

However, there are some other numbers that can be a little confusing, we’ll explain now those now.

1. Field of view

Naturally, the more you magnify something, the narrower your field of view will get.

When you look at the scopes’ specification, you will most likely see the list of parameters at different magnifications so that you can compare them with one another and with a human’s normal field of view.

Normal field of view of a human would be around 210 degrees.

Once again, spotting scopes have a much longer field of view than binoculars.

The bigger the field of view is, the wider the picture and the easier it is to spot and follow a moving object that you are observing. That is exactly why spotting scopes need a wider field of view.

Here is an example of a spotting scope’s field of view:

100 – 142 ft at 1000 yards

With this scope, you can see only 100th part of the field that you can normally see with your bare eye and at the 1000 yards distance.

2. Eye Relief

Eye relief is a measure that shows how close you have to bring your eye to an eyepiece in order to see the full picture.

A spotting scope of a lower magnification power would have a larger distance of eye relief while spotting scopes of a higher magnification power will make you come real close to the eyepiece so that you can see the full field of view.

Most of the spotting scopes have 16.7 – 17 millimeters listed for eye relief, which means that you can look through it at this distance and not lose the picture. If you go any further, you will not be able to see the picture.

Although it may sound uncomfortable to have your eye that close to an eyepiece, do not worry. Spotting scopes are made with this the eye relief distance in mind, so eyepieces are designed so that you can comfortably set your eyes that near to the glass.

The eye relief distance on spotting scopes is much more precise than the distance in some other scopes. For example, rifle scopes used in some other sports normally have an eye relief of 4 inches, which makes sense, since you do not want to have your face that close to something that you shoot from. Also, the magnification on rifles is not as high as magnification on spotting scopes.

Eye relief distance is also very important for people who wear glasses. If you are wearing glasses that are very thick, it can push your eye further away from the eyepiece, and you might not get the full field of view.

When you have it listed, you can calculate and understand the distance and the field of view much easier. In general, 12 to 16 millimeters of eye relief work just fine for everyone, even those with thick optical help devices.

3. Weight

Rather obvious, this is the total weight of a spotting scope. It is shown in kilograms or ounces.

Spotting scopes are usually really heavy and almost impossible to have in your hands for longer periods of time.

Normally, you would have a tripod to hold and support it.

This is why it is important to give a look at this number and determine whether your tripod can take it or not.

4. Exit Pupil

The exit pupil on a spotting scope shows the diameter of the light circle that enters the eye right from the scope.

An exit pupil that is too small will not give enough light to the eye’s iris and the image will be dim and blurry, while the one that has exit pupil too wide will just disperse the available light and waste it in vain.

Just as a guide, a human’s iris in normal light is 2 to 3 millimeters wide, 4 to 5 millimeters in low light conditions, and almost 6 millimeters in the dark.

However, not all of the scopes have this option listed, so it might be a bit harder to find this information sometimes.

5. Length

One more that is quite obvious, the length shows the length of a spotting scope from tip to the bottom and it is shown in inches.

Conclusion

Although numbers on spotting scopes (or any scopes in general) might be a bit confusing at first, they are very simple once you have them explained to you.

That is why we have made this simple guide for you and, hopefully, made shopping for a new scope easier and more understandable.

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