How Does A Telescope Work

How Does A Telescope Work – A Beginner’s Guide

Telescopes are a very fascinating thing, even for people with zero astrophysics interest. Who doesn’t want to sneak into one of those to see what’s outside our giant planet which is actually a very little one compared to its neighbours. This article is for those who are genuinely interested to know how a telescope works and what its functions are.

Before that, let’s do a little bit of an obvious introduction.

Telescopes 101

Telescopes operate by gathering and amplifying the light they collect from distant objects.­ Galileo Galilei is perhaps most renowned for inventing the telescope, and still being remembered for coming up with such an awesome invention.

The majority of telescopes, and indeed all the large telescopes, work by using curved mirrors to focus the light from the starry skies.

How Does a Telescope Work in the Night Sky?

It is hard to study objects in the night sky because they are so far away that makes them appear extremely dim. A telescope can collect more lights from distant objects than human eyes. As we collect more light with the telescope, we will be able to see these objects more clearly. 

Anyway, the first telescopes were designed to focus light by using large pieces of curved glass, the ones that are very commonly known as lenses.

Telescopes with high resolution are able to see dimmer things and are capable of seeing things that are far away. They contain mirrors or lenses known as “optics”. 

Larger mirrors or lenses can gather more light than small ones. Light is then focussed on the shape of the optics. When one looks through a telescope, the lights appear as a  shape coming from that speaking object. It is difficult to craft a perfect mirror, but even more challenging to make a perfect lens.

We are going to dive into detail in order to understand how a telescope works. But first, let’s look at a couple of terms to have a better understanding. I’m sure you’ve heard of them a million times,  but it’s time we knew them from a functional perspective.


A lens consists of a transparent piece of material that refracts light to form an image. Generally, the material is a transparent optical mineral such as glass or plastic. The process is different from simple lenses made out of glass which refract light using total internal reflection.


A mirror is a reflecting surface and the law of reflection explains the decision that, when a ray of light falls on the reflecting surface, the reflected ray is precisely on the same path as the incident ray and that the reflected ray has its angle of reflection, incident ray, and the reflected ray.

Different Types Of Telescope

Optical telescopes can be divided into three main types depending on the process of forming an image from light:

  • Refracting telescopes
  • Reflecting telescopes
  • Catadioptric telescopes

Refracting telescopes

A telescope in which lenses are used as the primary optics is called a refracting telescope. The lenses are always curved. A refracting telescope uses a series of lenses to gather light and form it into an image.

Reflecting telescopes 

Reflecting telescopes are telescopes formed by a combination of curved pieces of mirror and are designed to refract light and form an image. A lens needs to be thicker in order to bend light, but a mirror does not. A large mirror is not required to be thicker, but just the right curved shape is needed.

Reflectors can be used to examine both shorter or longer wavelength regions in the electromagnetic spectrum. When light enters a reflector, it usually reflects off the big mirror at the back; a ray then bounces off the smaller mirror near the front and towards the viewer. On reflecting telescopes, light is reflected back and forth from curved mirrors instead of being refracted straight through lens assemblies. Thus, reflecting telescopes are usually shorter, since the path that light takes is shorter. 

Catadioptric telescopes

A catadioptric telescope is an optical viewing instrument that is optimized for observations of distant astronomical objects and combines both refractive type optics lenses and reflective optics mirrors. 

The Maksutov telescope is an ideal example. 

The combination of both mirror and lens optics provides certain advantages, not the least of which occurs during manufacture. The term “catadioptric” denotes two separate words: “catoptric” which describes a technique that uses curved mirrors, and “dioptric” meaning one that uses lenses.

For more information about the types of telescope, click here.

More About How A Telescope Works

A telescope enables you to see a magnified image by using an eyepiece to project an enlarged or bigger image. Most of them allow you to change the amount of magnification using interchangeable eyepieces. 

However, as the magnification increases, the viewing area of the telescope decreases. Because of this, when you first locate an object in the telescope using the finder, it is best to center the object using the lowest power eyepiece in order to have the widest area through which to find the object from thereon. 

Once you have entered the sample, just switch to a higher magnification eyepiece to view the details better.

The telescope mount should be strong and sturdy to keep the telescope steady and to guide your telescope wherever it is needed. As you can see, the stars move from east to west across the sky. They are, consequently, in constant motion. So you have to move your telescope in the same motion because you can’t keep an object in view for longer than a few minutes without shifting the telescope slightly.

The mounts for telescopes come in two forms:

  • Alt-azimuth mounts
  • Equatorial mounts

Alt-azimuth mounts

Alt-azimuth mounts incorporate up-down and side-to-side motions in order to point the telescope. To track the movement of the stars using the telescope, however, you also need to accommodate up-down motion.

Equatorial mounts

An equatorial mount is a device that compensates for Earth’s rotation by having one axis of rotation parallel to Earth’s axis of rotation. Although equatorial mounts closely follow the Earth’s axis, they are complex. Some of these telescopes, nevertheless, are capable of tracking celestial objects for days and even weeks. This depends on whether the telescope includes motors to compensate for the terrestrial rotation so that an object can be monitored for less than one second without adjustment.

How To Choose The Best Telescope?

As you’ve come this far, I’m sure you would be interested to buy one for yourself. But, how to find the best telescope?

You must select a telescope by considering your individual needs. Before you buy a telescope, consider a number of things. Think about cost, portability, and what you think you’ll use it for. Then, think about  what you want to look at with your telescope. After your budget, the most important thing is your particular interest.

Telescope Pricings

The price is often one of the most important considerations when choosing a telescope. Because mirrors are cheaper to make than lenses, refractors are more costly to make than reflectors of the same size. 

On the other hand, a reflector generally provides a bit fuzzier image than a refractor. 

Refractors are geared toward amateur astronomers who appreciate viewing fine distinctions on planets; reflectors are used by people who like to take a look at faint objects in the sky.

To Sum Up

I hope it was an informative piece for astrophotography geeks like you. Telescopes are really fascinating. They can provide you great joy and fill up your thirst for watching the galaxy and beyond.

You will find a lot of informative articles along with buying guidelines on our website. Keep and eye on All Telescope Reviews!

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