What is a reflector telescope?

A reflector telescope is a telescope that uses one or more curved mirrors to form an image by reflecting light. Of these mirrors, the primary mirror is the most important, as it functions as the first and largest light gathering source. The primary mirror alone, or in combination with other mirrors, focuses the gathered light to the focus point, where the light is gathered on the secondary mirror. From the secondary mirror, the resulting image is redirected through the eyepiece, which contains a series of lenses, and from there to the eye.

What is the difference between a reflector telescope and a refractor telescope?

The basic differences between reflector and refractor telescopes is the kind of lenses that are used and how they manipulate the light that is gathered into the telescope. A refractor telescope uses two lenses to bend collected light in order to produce a magnified image. A large, or objective, lens, rests at the bottom and bends the light into the eyepiece, or ocular lens. The refractor telescope was the first type of telescope invented. The first refractor telescope was designed in 1609 by Galileo.

Sir Isaac Newton
Sir Isaac Newton

The first reflector telescope was designed by Nicola Zucchi at about the same time Galileo designed the refractor telescope. However, it didn’t work well due to the primitive nature of mirror grinding techniques of the time. When Sir Isaac Newton revisited the design in 1668, he overcame many of the problems with the reflector design by adding a secondary mirror at a right angle to the first mirror. The Newtonian design is still widely used in reflector telescopes.

What are the benefits of a reflector telescope?

One of the reasons reflector telescopes have grown in popularity is that its design allows a large amount of light to be collected for less expense than that of a refractor telescope. Many large telescopes use a reflector design, though extremely powerful telescopes tend to make use of hybrid designs that combine reflector and refractor approaches. The Hubble telescope even incorporates reflectors in its design.

Because of their lower expense for high magnification and resolution, reflector telescopes are a popular choice among hobbyists. Be sure to research extensively about the advantages and disadvantages of reflector telescopes before deciding on a final purchase. Having a telescope can open up a whole new world, so be sure you acquire one that will allow you to investigate that world as thoroughly as possible with your available budget.

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A Short History Of Reflector Telescopes

Reflector telescopes–those that use mirrors rather than glass lenses to gather and focus light–have been around since the latter half of the 17th century. 

Marin Mersenne
Marin Mersenne

The idea behind this type of telescope actually had its origins in the first half of the 17th century when Marin Mersenne, a French mathematician and philosopher, theorized in 1636 that the aberration of colours that occurs in refracting telescopes could be avoided by the use of two paraboloidal mirrors. He believed that such a telescope would deliver much more accurate colour representation since mirrors, unlike glass lenses, focus all levels of the colour spectrum at the same point. Persuaded by fellow philosopher Rene Descartes that the idea would never work, Mersenne never put his theory into practice.

James Gregory
James Gregory

In 1663, Scottish mathematician James Gregory built a telescope that used two concave mirrors–the primary one slightly hyperboloid in configuration and the secondary one more ellipsoidal in configuration. Light is gathered by the primary mirror, which reflects it onto the second mirror and then back again through a tiny hole in the primary mirror to the eyepiece. Although Gregory’s design is not unlike that used today for many reflector scopes, the one he built delivered a relatively disappointing image because of the low quality mirrors available at that time.

Robert Hooke in 1668 used multiple mirrors to build a significantly shorter telescope than had previously been the norm, and four years later Laurent Cassegrain improved on Gregory’s design by substituting a convex mirror as his secondary. 

The first truly successful reflector telescope was developed by Isaac Newton in 1668. Its three key components were a concave spherical primary mirror two inches in diameter; a flat, angled secondary mirror; and a convex eyepiece lens. Although Newton’s design was by far the best that had been offered by anyone up to that date, the quality of the mirrors available in the late 17th century still failed to deliver images as high in quality as its designer had envisioned. 

Reflector telescope technology took a major step forward in 1730 with the invention of the first parabolic and elliptic mirror by Scotsman James Short. Short’s mirror virtually eliminated all distortions, making it ideal for use in the reflector. The popularity of reflector telescopes grow sharply in the late 18th century when William Herschel developed a 40-foot scope using a mirror that was four feet in diameter. The use of such large-scale mirrors enable the gathering of vast quantities of light, far more than could possibly be gathered using a telescope of refractor design. 

Although the quality of reflector telescopes has steadily improved with the availability of higher quality mirrors, the basic design of these scopes is not significantly different today than it was in the 18th century.

Where To Use Your Reflector Telescope

Serious students of astronomy–or those who aspire to be–generally recognize that the best type of telescope for their needs is a reflecting scope, one that gathers and focuses light with two or more mirrors. Because its primary mirror is greater in dimension than the glass lenses of refractor scopes, the reflector telescope can usually shed more light on the objective image than can possibly be gathered using glass lenses of much smaller diameter.

As with almost all products, reflector scopes come in a variety of sizes and–more significantly–qualities, so you must shop carefully to get the very best buy for your money.

One of the primary advantages of reflectors vs. refractors is the virtual absence of chromatic aberration–or the distortion of colors–that is generally experienced with refractors but is eliminated in the reflector because the latter’s parabolic mirrors focus each ray of light received from the original parallel beam at a single point. While the mirrors of a reflecting telescope in no way alter the wavelengths of light, the same cannot be said of refractive lenses, which by definition alter the way that the original wavelengths of light are eventually perceived. 

what is a reflector telescope

Most users of reflecting telescopes feel they are getting more bang for their buck in that the use of mirrors offers significantly more magnification power than a refractor scope of comparable price. Because only the reflective side of the mirror interacts with the light, the optical surfaces in a reflector can be produced more inexpensively than the glass lenses of a refractor, the surfaces of which must be perfectly polished on both sides to allow light to pass from one side of the lens to the other without any intervening distortion. 

Although most astronomers–both of the professional and armchair variety–prefer reflecting telescopes, both types of scope have some drawbacks of which users should be aware. In the case of reflectors, users must take care to maintain their scopes on a regular basis to ensure that the mirrors are in proper alignment and kept scrupulously clean. Failure to do so almost guarantees that the images captured by the scope will deteriorate in quality over time. 

Another problem shared by both reflector and refractor scopes is the fact that both deliver an inverted image. This problem can be easily enough addressed by introducing a relay or prism into the light path so that the final image perceived at the eyepiece is converted back into its original position. 

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Caring For Your Reflector Telescope

Reflector telescopes are a bit more fragile than most refractor telescopes. The mirror is extremely sensitive to scratching and debris; therefore, it is imperative to keep it clean by gently scrubbing it with a soft cloth and minimal solvents. Furthermore, aligning the mirrors with a laser should be done on a daily basis. Many choose refractor telescopes because of maintenance issues on reflector scopes, but there are certainly some perks to owning a reflector telescope. Every telescope is delicate and requires careful maintenance, but reflectors need special care; one reason might be because there are only two thin fragile mirrors that need alignment in a reflector. Make sure that the tubing is covered when not in use. 

Here are some crucial steps for cleaning a reflector telescope:

Basically, if a reflection is visible in the mirror, it is not necessary to clean it. Remember, the machinery is delicate; if smudges and scratches are present–apply a soft cloth and rub the surface gently. Perhaps a better method for removing some stubborn dust and other offensive particles is to use a can of in order to blow it at the surface, thus preventing additional scratching that can occur with rubbing.

Secondly, remove the mirror and wash it with warm water. Do not touch the surface; just allow the water to run over it. This will remove all loose particles, but with stubborn dirt, rubbing may be the only solution.

Next, find an extremely mild solvent, and if one is not available, simply dilute dish detergent. Use the softest cloth available; perhaps cloth used for cleaning glasses is the best bet. Do not use typical tap water because of the excess residue. So, unfortunately, dipping into the stash of bottled water is crucial for proper cleaning.

Finally, place the mirror on its side allowing moisture to roll off of it. Wait until it is thoroughly dry before placing it in the telescope again. It’s crucial to minimize scratching because it will dramatically affect the telescope’s functionality.

Enjoy the fact that reflector telescopes do not suffer from the same ailments that refractors suffer. The user will not have to deal with chromatic aberrations. Moreover, reflectors are less expensive. Most astronomers choose reflector telescopes, but the drawback is the incessant realigning of the mirrors.

Another advantage regarding maintenance on a reflector telescope is that there are fewer components than refractors, and less chance of causing severe damage.

Reflector vs Refractor Telescopes

There are two primary types of telescopes, namely refractors and reflectors. The third type– the catadioptric or compound telescope–is simply a combination of the two. Both reflector telescopes and refractor telescopes have certain perks and drawbacks, but both of them serve essentially the same purpose; they simply go about it in different ways.

Refractor telescopes have been around since the early 1600’s. They were notably used by Galileo and Kepler, and they are still a common find in the telescope market. Refractors operate under the same principle as binoculars. A convex class lens is placed inside the end of a tube. This lens collects and bends the light that enters it to a central focal point. Another, smaller lens at the opposite end of the tube acts as the eyepiece, and magnifies this image. Thus, when the telescope is focused on a light reflecting object, the image appears larger and clearer. 

Reflector telescopes, on the other hand, were created nearly eighty years later by astronomer and physisist Sir Isaac Newton. Instead of passing light through glass at the front of the tube, reflectors reflect light off of a mirror placed in the back of the tube. The image is typically then reflected off of a smaller mirror placed inside the center of the tube, and directed through the eyepiece somewhere on the side of the telescope. More recent models allow the secondary mirror to reflect the image through a small hole in the objective (primary, larger) mirror, so that the eyepiece can be located at the back of the telescope. Both the Hubble Space Telescope and the Keck Telescope are recent examples of reflectors.

Refractor telescopes, because they are closed at both ends by lenses, tend to be less susceptible to atmospheric changes and elements. This makes them a bit more reliable and consistent. Unfortunately, because refractors rely on bending light to create an image, chromatic aberration may occur. This means that images may appear to be discolored, or may be incircled by rainbow colored rings.

Furthermore, very few large refractor telescopes are available. The objective lenses for refractor telescopes require large amounts of time and energy to create. The glass for the lens must be ground to a perfect shape, or the telescope will not work correctly. As lenses grow larger, the glass can become heavy and even more expensive to procure. For the amateur stargazer, however, there are usually no immediate problems with small refractor telescopes.

Reflector telescopes, because they are open at the top, are more likely to fall victim to elemental changes and dust. They require more upkeep than refractor telescopes. It is also necessary to align or “collimate” the optical pieces on a reflector telescope, which can be a confusing process for the beginning astronomer. Finally, while images viewed through reflector telescopes do not suffer from chromatic aberration, images in the mirror’s periphery may undergo coma, a sort of stretching of the object in view.

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What is a reflector telescope: more

The reflector telescope also known as the Dobson/Dobsonian or Newton/Newtonian is the best telescope for beginner astronomers. It is very easy to use and it is inexpensive. You get the high quality without the expensive price tag. Once a person becomes a little more experienced they can add different mounts and eyepieces and eventually move on to an advanced model. For the beginner the reflector telescope will allow them to see the moon, sun, stars and the galaxies.

What to Look for

When searching for a reflector telescope it is best to find one with the largest optical quality that you can afford that way you will be able to see the smallest objects the farthest away. A large aperture is the scientific term for the scope of the lens. Also try and purchase a design that is multipurpose. Also the accessories are a necessity, the mount and the eyepiece. Be aware that with the reflector scope you will need to adjust the mirrors occasionally for equal alignment. Instead of a lens this scope uses mirrors to refract the light. Remember that if you are unsure of how to adjust or change anything refer to your owners manual or someone that is fairly educated in the use of telescopes. Make sure to try out different scopes if you are able to and make an intelligent decision. Bring someone that has experience with telescopes along to help you make your decision.

Locating the right telescope 

A reflector scope can be purchased from any reputable retailer online or a physical store. It can also be purchased from telescope sites. The best place to learn more about your telescope is to look into several sites on the web like NASA, Space sites, telescope sites, blog sites and history sites. Another place is the library or a local bookstore that has books on telescopes and gives you details on how to care for your particular type of telescope.

A reflector scope is excellent to start with on your journey through astronomy and it will give you the pleasure and quality that you need. It is inexpensive and it has good optical quality, and it has good distance ability. It has the ability to reflect the light using mirrors instead of a lens, and it is the best beginner scope that you will be able to find that will not take away from the purpose of the scope.

Last update on 2020-07-15 / Affiliate links / Images from Amazon Product Advertising API