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Whenever it comes to a telescope, you will definitely find the word “eyepiece”. The eyepiece is not just a word or something additional. It's a major part of a telescope whatever the scope is. The eyepiece is that piece of a telescope where you will keep your eyes to observe the objects. 

Basically, an eyepiece is located at the edge of a telescope tube and it can be changed before each observation. You can't imagine that the most interesting and significant thing is how the eyepieces work. 
Well, probably you know the focusing method or observing process of a telescope. But it will not be surprising if you don't know exactly how the eyepieces work in a telescope, how they play roles, what their features are. Here we have explained these things clearly. But before going through the detailed process, you might want to know the very primary things about an eyepiece. Just keep your eyes in.

What Are Eyepieces?

Eyepieces are designed by optic lenses that are used in various optical devices. Eyes are kept here to observe the spotted objects through the device and that's why they are called “Eyepiece”.

Generally in a telescope, an eyepiece is of short focal length that works to magnify the targeted objects and show a virtual image to the observer. Different types of eyepieces are designed to show different objects. The best images are produced by low-magnification eyepieces whereas normal views are the result of high-magnification eyepieces.

How the Telescope Eyepieces Work

How Do the Telescope Eyepieces Work

Telescope eyepieces work by producing virtual images using their focal length along with the help of other mirrors or lenses. Besides, there are some tricky things that are obvious for an eyepiece to work.

  • First, they magnify the spotted object to produce a sharp image. 
  • When the image is in focus, they provide comfortable eye relief by maintaining the length issue.
  • Then their target is to determine the apparent field of view or the amount of sky.
  • Finally, they help you to see the produced images that are created by the reflection or refraction of light in the mirrors or lenses.

Sounds difficult? Just scroll down and you will get a clear explanation of the whole process in detail. 


Telescope eyepieces work by producing virtual images using their focal length along with the help of other mirrors or lenses. Besides, there are some tricky things that are obvious for an eyepiece to work.

Eyepieces mainly work by magnifying the image of the object. When it comes to magnification, there are two focal lengths. 

1. The focal length of the telescope

2. The focal length of the eyepiece 

In the eyepiece, this focal length is calculated by millimeters. You will find this number written on the edge of every eyepiece. It is required to know the magnification your eyepiece will give you combining with that of a telescope. Seems complicated? Well, it's not complicated at all. Just a simple thing, a division you need to do. Divide the focal length of your telescope by the focal length of your eyepiece. 

So, the less your eyepiece focal length, the higher magnification you get, and the bigger your eyepiece, the less magnification you get. Suppose, you have an eyepiece with a focal length of 10 millimeters and a telescope of 1600 millimeters. Now after dividing, the magnification will be 160 times. But if you have a focal length in your eyepiece of 20 millimeters, it will be 80 times. And also, that eyepiece of 10 millimeters can give different magnification on another telescope. In this case, it depends on the focal length of your scope.

Though, the magnification range mostly depends on the scope you are using. Still, there is a usual range that is from 50x to 250x. 

Eye Relief

Eye Relief

Another important thing in the eyepiece working method is eye relief. The distance between your eye and your eyepiece is called eye relief. If your eye relief is not much longer, your eyepiece won't give you a clear view and it will be difficult for you to observe.

When you wear eyeglasses, eyepieces that have short eye relief will not suit you. It won't be possible for you to watch. In that case, use long eye relief eyepiece

Generally, eyepieces that have long focal lengths will automatically provide you long eye relief. But the short length eyepieces don't inherently have long eye relief. They need to be designed in such a way that they can give you long eye relief and clear observation.

Field of view

How much sky you are observing using an eyepiece depends on two things:

  1. Magnification
  2. Apparent field of view

Basically, apparent field of view is a part of your eyepiece. Eyepieces are designed by two types of apparent view, narrow and wide. When you will not change the magnification, that means when you keep the focal length unchanged and use an eyepiece of wide apparent view, you will see a wider true field observation. 

On the other hand, if you change the magnification keeping the apparent field unchanged, you can enjoy a wide field of view by a low-magnification eyepiece. 


If you want to observe a very large object such as the galaxy or the star cluster, you need a wide field of view with a low-magnification eyepiece. Don't forget that field of view matters when you want to enjoy the best images.

Why Are Eyepieces Necessary?

Eyepieces are necessary for a telescope because our eyes are not capable of producing images of a distant object that is possible by an eyepiece as eyepieces are made of lenses. 

To be more specific. We know that a telescope works in an optical system and a camera also does. A camera creates an image by a camera lens. Similarly, a telescope works by the lens. And that lens is your eyepiece.

Yes, you can use a camera too for creating images. But think, if you use your eye instead of a lens, will your eye create an image? The answer is obviously No. You know why? Because your eye isn't able to produce a virtual image focusing on a real image. But your eyepiece is able to do. Thus an eyepiece is the key part of a telescope. 


Telescope eyepieces help you to observe sharper, brighter, and magnified images. We revealed the method in detailed words how an eyepiece works. If you are not clear yet or interested to know more, ask us. Let us know if we need to add more here. Leave your queries and share your thoughts. We would love to reply to you.