Optics Mag is reader-supported. When you buy via links on our site, we may earn an affiliate commission at no cost to you. Read more.

What Is a Refractor Telescope? An In-depth Explanation

Last Updated on

Refractor Telescope

Few inventions have transformed the way that we view the universe and our place in it like the refracting telescope. From the first time that Galileo pointed a refractor telescope to the sky to every time a scientist does the same thing today, it opens up an entirely new world to observe.

But what exactly is a refractor telescope, and how does it work? It might seem like magic when you look through the eyepiece, but it’s all science! Keep reading, as we break it all down for you here.

telescope divider 2

How Does It Work?

A refracting telescope works by using two convex lenses: the objective lens and the eyepiece. The objective lens sits at the front of the telescope, and its convex design bends the light toward a single point inside the telescope.

The eyepiece is the piece that you look through, and it bends in the opposite way of the objective lens. The curvature of the eyepiece is concave, and it picks up the light right at the point where the objective lens bends the light to, also known as the focal point.

It might not make too much sense unless you dive into the practical details of how light works when it shines through different surfaces, but basically, refractor telescopes take full advantage of these scientific properties to increase the size of an image.

What Are the Different Types of Refractor Telescopes?

 

When Galileo invented the refracting telescope in 1609, it was a crude design and only had a magnification range of 8 to 20.

We’ve come a long way since then, even if we use the same principles that Galileo first used. Modern refracting telescopes have a more complicated design for the objective lens to achieve higher magnification without sacrificing image quality and resolution.

When it comes to modern refractor telescopes, there are only two types to consider. The first is the achromatic refractor telescope. The term “achromatic” refers to the type of lens in the front of the telescope.

An achromatic lens uses two pieces of glass meshed together for the objective lens in the telescope. The first piece is called the “crown glass,” and it’s a convex design. It meshes with the “flint glass,” which is concave, and they work together to help remove distortion and provide a quality image.

However, this design isn’t perfect, and it’s why the best refractor telescopes today use an apochromatic design. This corrects the wavelength issues of the achromatic design by adding another convex lens behind the concave lens, which now has a concave design on both sides.

That said, apochromatic reflecting telescopes cost more than achromatic ones.

Where Is It Used?

Today, you can find refracting telescopes just about anywhere. They’re common in amateur backyard telescopes, and you can also find them in massive observatories, like the Yerkes Observatory, which has the largest refracting telescope in the world — it has a 40-inch objective lens!

You can get a refracting telescope for under $100 on Amazon, or you can go with a higher-priced option with more features and capabilities. The point is that refracting telescopes are all over the place; if they’re the right choice for you depends on what you’re trying to view.

Refracting telescopes do a phenomenal job of producing high-quality images with great contrast and sharpness, making them outstanding for terrestrial viewing.

However, since there’s a limit on how large you can make the objective lens, they’re not great for viewing fainter and more distant objects.

Advantages of a Refractor Telescope

Refractor Telescope

Image Credit: KAZLOVA IRYNA, Shutterstock

Refractor telescopes do a great job in many areas, and it’s why they’re so popular. They produce a high-quality image and are typically lighter and more transportable than most other telescope options.

They also use a completely closed tube setup, which means the chances of dust or humidity creating any problems are virtually non-existent, and there are almost no maintenance or cleaning requirements.

Disadvantages of Refractor Telescope

While there are many advantages to refractor telescopes, there are significant drawbacks too. First, they have a small diameter, which dramatically decreases the amount of light that they can bring in.

Second, both low- and high-end models often have chronic aberration. This puts a color fringe around a bright object that you’re viewing, even if there’s no colored fringe there.

telescope divider 2Frequently Asked Questions

Here are the answers to the most frequently asked questions about refractor telescopes.

What Is the Best Use for a Refracting Telescope?

You can use refracting telescopes for many things, but the best use for them is probably planetary viewing within the solar system. If you’re trying to view Jupiter, Mars, or Saturn, that’s the perfect opportunity to pull out a refracting telescope.

 

What Type of Telescope Is the Hubble Space Telescope?

The Hubble Space Telescope is a reflecting telescope, not a refracting telescope. In fact, the mirrors led to the infamous culmination issue shortly after NASA brought it into service.

What Type of Telescope Is the James Webb?

The James Webb Space Telescope is a reflecting telescope. Since the primary purpose of these space-based telescopes is to see far-away objects, it makes sense that the manufacturer used a reflecting design instead of a refracting one.

Which Is Better: a Refractor or Reflector Telescope?

It depends on what you want to view. If you want to view bright or close objects, like planets or binary stars, a refracting telescope is probably the way to go. But if you want to view distant stars, galaxies, or nebulas, a reflecting telescope is what you want!

A Quick Reference Guide

Advantages of Refractor Telescope Advantages of a Reflecting Telescope
Sharp images Brings in more light
Small, compact, and lightweight Less expensive for more powerful telescopes
Typically requires no maintenance High magnification range

telescope divider 2Conclusion

The refracting telescope was the first type of telescope that humans used to view the stars, and it’s still one of the most popular options today! Scientists may have made a few tweaks along the way, but the principles remain the same, and it’s still great for magnifying objects!

You might be interested in:


Featured Image Credit: Tim Gouw, Unsplash

About the Author Robert Sparks

Robert’s obsession with all things optical started early in life, when his optician father would bring home prototypes for Robert to play with. Nowadays, Robert is dedicated to helping others find the right optics for their needs. His hobbies include astronomy, astrophysics, and model building. Originally from Newark, NJ, he resides in Santa Fe, New Mexico, where the nighttime skies are filled with glittering stars.

Robert Sparks Profile Picture