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 Reflecting Telescope? How Does It Work?

Last Updated on

reflecting telescope on the ground

The first reflecting telescope was designed by Sir Isaac Newton as an alternative to the refracting telescope, which suffered from severe issues such as chromatic aberration. This unwanted effect is observed when the lens fails to focus all the colors to the same point, causing the resulting image to distort. The reflecting telescope solved this issue, and now a large portion of telescopes used by astronomers, researchers, and engineers fall into this category.

One great example of this design is the Hubble Space Telescope, a low earth orbit resident that serves as a vital research tool. Another example is the James Webb Space Telescope, which is the most powerful telescope to ever be launched into space. By using infrared astronomy, the James Webb Space Telescope is able to see further and better than anything before it. This is what makes reflecting telescopes such a popular choice among all levels of stargazers.

binoculars 3 divider

How Does a Reflecting Telescope Work?

Unlike other models, reflecting telescopes use mirrors to collect and focus the light instead of lenses. Capturing the highest quality image requires extreme mathematical precision, so these mirrors must be shaped to within minuscule tolerances. Any imperfections in the mirror’s surface could distort the resulting image, so using them is advantageous because they’re easier to shape than lenses.

Mirrors also suffer less spherical aberration, which is an unwanted scattering of light when lenses aren’t perfectly aligned. Because reflecting telescopes are comparatively inexpensive to make, the mirrors can be made very large, which makes them ideal for reflecting lots of light and looking deep into space.

What are the Different Types of Reflecting Telescopes?

Newtonian Telescopes

newtonian telescope

Image Credit: AstroStar, Shutterstock

Newtonian telescopes, also known as Newtonian reflectors, are a type of reflecting telescope invented by Sir Isaac Newton, an English scientist well known for his discoveries in optics and mathematics. Newton completed his first reflecting telescope in 1668, which sported a simple design that is still popular today.

What makes Newtonian telescopes advantageous is that they are free of chromatic aberration, which is caused by the lens not focusing all  the colors to the same point. Newtonian telescopes are also less expensive as only one of their optical elements needs to be polished into a complex shape within narrow mathematical precisions. The eyepiece of a Newtonian telescope is also located at the top, allowing for a more compact and portable system.

However, transporting your Newtonian telescope can be a problem, as the shocks associated with this often move its optical elements out of alignment. This can prove to be annoying because it  meansrealigning your telescope every time you set it up.

Cassegrain Telescopes

cassegrain telescope

Image Credit: Allexxandar, Shutterstock

Cassegrain telescopes have been around since 1672 and are attributed to Laurent Cassegrain, who was a Catholic priest. Classic Cassegrain telescopes utilize a parabolic primary mirror and a hyperbolic secondary mirror that reflects the light through a hole in the primary mirror. When the light enters the hole, it converges to a focal point at the eyepiece.

This is unique as the “folding” behavior of the light effectively increases the focal length of the otherwise mechanically short telescope. Cassegrain telescopes are excellent for deep sky imaging, planetary observation and are considered an “all-purpose” telescope. This type of reflecting telescope can produce excellent high-contrast images, making them popular with intermediate to advanced stargazers. All Cassegrain telescopes tend to be much more expensive than their Newtonian counterparts with the same aperture.

Advantages of Reflecting Telescopes

Cost

The mirrors used to focus the light in a reflecting telescope are far easier to construct than lenses. Optical glass lenses must be completely clear so that light passes through them completely. They must also meet a variety of other precise criteria, making them extremely expensive to produce. Mirrors, on the other hand, are relatively inexpensive to produce and deliver more magnification power than refracting telescopes.

Size

Since the mirrors in a reflecting telescope are comparatively easy to produce, they can be made very large, allowing them to reflect a lot of light. This makes reflecting telescopes ideal for space-based applications because they allow us to see incomprehensibly far and understand the origins of the universe. Mirrors can also be rigidly constrained to the telescope as only one of their sides is necessary for reflecting light.

reflecting telescope

Image Credit: Yes058 Montree Nanta, Shutterstock

Disadvantages of Reflecting Telescopes

Maintenance

Reflecting telescopes are prone to a slew of maintenance issues and must consistently be cleaned due to their open design. Cleaning the sensitive mirrors also tends to misalign them, which is expensive to have fixed. Some mirrors are even coated with silver, which can tarnish in the open air. This requires you to polish your mirrors periodically and fully replace them within a few years.

Frequently Asked Questions (FAQ)

Is a Reflector or Refractor Telescope Better?

Reflector telescopes are popular among intermediate and advanced stargazers but are also great options for amateurs. They are a great low-budget solution for a high aperture scope because they can have large reflectors. Reflective telescopes are great if you want to capture bright celestial bodies like the Moon, Saturn, or Venus.

On the other hand, refractor telescopes are an excellent choice for deep space observations, astrophotography, and viewing galaxies and nebulas. Although refractive telescopes are recommended for new beginners, they can get quite pricey as their aperture goes up.  At the end of the day, the best telescope for you really boils down to your preferences and observation habits.

newtons reflector telescope

Image Credit: milosgagic, Shutterstock

Why Are Reflective Telescopes Better for Observing Planets?

Reflective telescopes are the primary choice when a planet is to be imaged or observed. This is because the longer effective focal length of reflective telescopes makes it easier to align the mirrors within a minuscule tolerance. Having your mirrors perfectly aligned is important because it helps maintain image quality even at high magnifications. In addition, reflective telescopes produce high contrast images which make it easy to discern the intimate details of the planets.

binoculars 3 divider

Conclusion

In summary, reflective telescopes are a great option for beginners and advanced stargazers alike. They are much more powerful, budget-friendly, and stable than their refractive counterparts. Reflective telescopes are great for observing bright objects in the sky such as the Moon, Venus, and Saturn due to the beautiful, high-contrast images they can produce.

Some of the most powerful telescopes in the world such as the Hubble and James Webb Space Telescopes are reflective telescopes, which are both pushing the boundaries of our frontier in space. This beginner-friendly telescope is sure to get anyone excited about astronomy with the incredible details it pulls out of the night sky.


Featured Image Credit: Yes058 Montree Nanta, Shutterstock

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