There are two main kinds of telescopes that can be bought for personal use: reflecting and refracting. While they sound similar they have two different methods with their strengths to magnify the night sky.
Telescopes work on the principle of magnifying a distant object in a way that is clear and natural to observe.
In both reflecting and refracting telescopes, light is gathered and focused on a single point where a human eye can see it better than it could on its own. Both kinds of telescopes use different methods to achieve this same goal.
The first telescopes were refracting in nature and were later adapted to have a reflective variant. Today, both kinds of telescopes can be widely found in scientific and casual settings.
So how does each work and is one better than the other?
Refraction: Lend Me Your Lens
The most common kind of refraction that is observable in daily life are glasses and contacts. Refraction is the magnification method that uses curved glass or plastic to capture light and magnify the desired image.
These lenses are made specifically to certain shapes to capture light and create a desired magnifying effect.
Glasses are designed to correct certain vision problems usually at a distance of about twenty feet from the wearer.
Refracting telescopes work on the same principle but they are trying to gather images from much farther away and therefore must be much larger. Unlike glasses, refracting telescopes usually have two lenses: the objective lens and the eyepiece.
The objective lens is the larger of the two lenses and is the one which would be pointed at the sky. The eyepiece is the second lens which is used for viewing. These two lenses work together to give the user the desired magnification.
Refracting magnification is calculated by dividing the focal length of the objective lens by the focal length of the eyepiece lens.
The objective lens will usually be a static piece of a refracting telescope with the option to change out different size eyepieces to get different magnification levels.
For example, a large magnification is not necessary when looking at the moon compared to trying to see the rings of Saturn.
It’s not all about the Magnification
A common belief is that magnifying power is the most important aspect of a telescope.
Magnification is important but so is image clarity. A low-resolution image will remain low resolution even if you continue to zoom in on it and in a lot of cases magnifying a low-resolution image makes the resolution worse.
To get the highest resolution possible when viewing the sky, you want the largest light gathering potential possible which is directly related to the size of the objective lens.
Scientific and commercial telescopes have massive objective lenses to gather as much light as possible.
Two Lenses, Two Thumbs Up?
Refracting telescopes are relatively easy to use, they are easy to find and they work. They have been around in some form for over 400 years and they are based on proven science.
Their biggest downside has to do with image quality, which has to do with the physics of refraction.
Since refraction is based on bending light it creates a distortive effect which is called chromatic aberration.
Anyone who has seen a rainbow or messed around with a prism in their life is familiar with the idea of chromatic aberration. White light, like the light from stars, can be split into many different colors when refracted.
Chromatic aberration occurs when looking at bright objects through the lens. It creates a rainbow glow around objects which is due to the light being split up as it passes through the lens.
While this is more distracting than anything it does affect the image quality of refractive images, especially bright ones.
It is wild to think about light coming off of stars hundreds or thousands of light-years away, passing through vast distances of space and being split up in a telescope on earth and hitting a human eye after who knows how long?
The light from some of these observable stars left their origin point at the time of the Roman Empire!
Overall, refractive telescopes are simple, proven and customizable. Eyepieces can be bought and configured for different levels of viewing and magnification.
There are even ways to try and fix chromatic aberration but they can be complicated or pricey depending on the option. The image quality is good overall and perfect for in solar system observation.
Reflection: Mirror Mirror In the Tube
While refracting telescopes use curved lenses to gather and focus light, reflective telescopes use mirrors to do the same task. This is possible due to the physics of light over long distances. Don’t worry, this time the light is not going to be split up into a bunch of colors.
When light travels over vast distances in a vacuum they straighten out into single rays. Given enough time and distance, rays from a single origin point will become parallel to each other. No light rays will bend or cross one another from a single light source over the crazy distances of space.
Everything that a telescope would be used to observe is far enough away that all of the light from these objects will be parallel allowing the reflecting telescope to work.
Instead of bending light using lenses, reflective telescopes use mirrors to reflect the light through a parabola to one single point. Imagine someone using an aluminum screen to magnify the sun’s rays for tanning, that is the reflection principle.
Sir Isaac Newton was the first person to invent the reflective variant of the telescope in the late 1600s.
He positioned the objective mirror at the base of his telescope and then placed a secondary mirror near the top of the tube that reflected light upwards at a 45-degree angle into an eyepiece.
This way there would be no interference from the user on the light rays during use and virtually eliminated shadows from the equation.
Are Reflective Telescopes the Fairest of Them All?
Reflective telescopes are light and easy to handle due to their design. They produce crisp images and are easy to find in many different sizes and price points. The Newtonian variant has been in continuous use for four centuries and comes with a long history of amateur sky-gazing use.
The biggest drawbacks to the reflective telescope are the mirrors themselves. They are generally fragile and can sometimes be easily dislodged or moved from its place. If the position of the mirrors is messed up it can be very hard to get them right again without damaging the fragile pieces of the telescope, especially for true amateurs who are just starting.
Also, many reflecting telescopes have one end open to the night sky to collect light for the mirror. This open design can lead to dust, bugs and other unwanted objects to enter the telescope which then requires cleaning to keep that good sharp image everyone loves.
Reflective telescopes, on the whole, are of sound design and preform their duties extremely well. If you are comfortable keeping them from getting dirty or misaligned then they will serve admirably and can give some truly spectacular views of the galaxy, especially distant objects.
Refractor vs Reflector: Which To Choose?
From their long histories and continued use, it is easy to say that both of these telescope designs have proven their worth over the years. Choosing one is just a matter of preference based on a few key differences for their applications.
Refractor telescopes are generally hardier than reflector telescopes so if you want to collapse your telescope and take it with you while camping or hiking to look at the night sky in remote places it would generally do better than a reflecting telescope.
If you are going to keep the telescope in a designated spot in the backyard and use it that way then a reflector telescope would do just fine.
Reflector telescopes eliminate the chromatic aberration that plagues all refractor telescopes but refractors will generally have a clearer overall image quality for objects that are closer to the viewer.
If you want to try and see deep space objects such as specific distant stars, other galaxies, and nebula then a reflector telescope will probably be your best bet. If you want to look at the planets in our solar system and their moons and nearby stars then a refractor telescope will be more suitable.
Factor In the Price
Price is an important factor and both of them start at around the same price point in the lower quality range.
As you get into more intermediate to expensive telescopes reflectors get cheaper for their magnification due to their simple design, a mirror is much easier to produce than a specific lens.
However, the more expensive refractors have more accessories and customization options such as eyepieces and prisms that can be attached with ease making it an individual preference based on what the telescope is going to be primarily used for.
When it comes down to it, there are no wrong answers or wrong choices. If one of these two designs was objectively better than the other then one of them would have made the other obsolete by now but they both coexist because they are both great devices for observing the sky.
Decide which one sounds like a better fit for your sky-gazing needs and make a decision, either way, you’ll be using a design favored by Galileo or Newton.