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When a beginner starts to learn about astronomy and telescopes, he gets introduced to the types of telescopes: reflectors and refractors, their designs, features, and how they work. The same thing might go for you. After getting introduced to the very basics of refracting telescopes, you will probably look for the method of how a refracting telescope works. That's why we have arranged this article. Stay with us and get the whole thing clear. First, let's know about a refracting telescope.

What is a Refracting Telescope?

Refracting telescope is an optical instrument that uses specifically designed lenses to produce clearer images by bending the light into the focus. Thus an image of a distant object comes to be visible. Refracting telescopes are mainly used to observe the moon, the stars, or the planet.

A Refracting telescope is smaller, more lightweight, and portable than other telescopes. But still, it is long relative to its size as it needs to be. To know the reason behind this and to learn the process of how a refracting telescope works, you need to know about its design.

Design of a refracting telescope

Design of a refracting telescope

There are two lenses in a refractor: the objective lens(larger) and the eyepiece lens (smaller). The objective lens is for focusing whereas the eyepiece is for viewing. The first lens is at the end of the tube. The second one or the eyepiece is at another side, closer to your eye. These two lenses are designed in a convex shape and that's why they are called convex lenses.

While observing through a refractor, the light that comes from an object needs to flow in a straight way through the optical tube and reach the eyepiece. If it can't flow directly, it might not go to the eyepiece where you keep your eyes. As a result, you can't observe the object. The larger the lens, the longer the tube needs to be. Otherwise, it can't bring the images into focus.

How a Refracting Telescope Works

How a Refracting Telescope Works

A refracting telescope works by using its two lenses that are the curved pieces of glass. The first lens refracts light from a distant object by bending it and makes a virtual image of the object closer to your eye than its real position. Thus a refracting telescope has the effect of magnifying an image tricking your eye in considering the object closer than it really is.

Now let's come to the detailed process.

  • First, the light rays come at a parallel from a targeted object and refract on the first lens of the tube. A real image is formed here, at the objective lens.
  • Then the light straightly passes through the tube and goes to the secondary lens or the eyepiece.
  • The primary or the objective lens works to gather light as much as possible and the eyepiece does the magnification.
  • That means when the real image comes into focus, the eyepiece widens or magnifies it into a virtual image so that it can be visible to the retina of your eye.

Note: As the magnification occurs in the eyepiece, you can change it according to your demand whether you want less power or need maximum power.

Why can't you observe through your eyes?

Your eyes are not capable of producing images of a distant object and that's why you can't observe a magnified image through your eyes. 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.
So you can use a camera lens or a telescope eyepiece. But think, if you use your eye instead of a lens, your eye won't create an image. Because your eye isn't able to produce a virtual image focusing on a real image. But a lens or an eyepiece is able to do so. This is the reason you are unable to observe through your eye.

What Does a Refracting Telescope Do?

Basically, a refracting telescope focuses on an object to produce a sharp image. Let's see at a glance.

  • A refracting telescope is used in astronomy to observe things.
  • It bends the light passing through the tube.
  • It makes the image clearer and visible to your eye.
  • A refracting telescope mainly makes the faraway things closer to you such as the star, the moon, or the planet.

Refracting Telescope Diagram

Refracting Telescope Diagram

It's a refracting telescope diagram. Here, from this diagram, you will notice two focal lengths.

  1. The focal length of the telescope
  2. The focal length of the eyepiece

You will also notice the distance between the objective focal length and the eyepiece focal length. And it is calculated as the sum of the focal length of two lenses. Let's be more specific.

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.

Advantage & Disadvantage of Refracting Telescopes

Refracting telescopes has both advantages and disadvantages. But if you compare, the positive sides will be more than the negative sides. Let's see.


  • Transportable and lightweight
  • Not necessary to clean or manipulate
  • Incredible sharpness with great contrast
  • No chance to be dirty as the tube is closed


  • Not enough light collected
  • Expensive


This article showed how a refracting telescope works, what a refractor does, the diagram of a refractor, the advantages and the disadvantages of a refractor and more specific things. We have discussed every of your required information to make the things clear to you. Yet if you have something to know, ask us. If you have anything that is supposed to be better to add in this article, let us know. Share your opinions and drop your queries.