It is common for beginner astronomers to get stuck between reflector or refractor telescope when selecting their very first telescope.
At the heart of it – A telescope gathers and focuses light from the distant object to see a magnified image.
Now there are two ways of making the light focus at a point. One is by using a curved mirror, or by passing the light through a lens.
Since Mirrors reflect light. A telescope that uses a mirror as its primary objective is called a reflector telescope, or simply reflectors.
Similarly, a Lens refracts light, and a telescope that uses a lens as its primary objective is called a refractor telescope, aka refractor.
So what are the advantages and disadvantages of using a mirror over a lens in a telescope?
What could you expect to see in the night sky using these scopes? and which of the two telescopes you should get as a first-time buyer?
These are some of the questions we will answer in this detailed Reflector vs Refractor telescope comparison. We will also introduce you to the third type of telescope that uses a combination of both lens and mirrors.
By the end of this article, you will be well equipped with everything you need to know in order to select your very own telescope.
Types of telescopes and their brief history
Both reflectors and refractors have been widely used by astronomers for observing the night sky as well as for astrophotography.
Refractor telescopes are some of the first telescope designs. It was used by early astronomers such as Galileo Galilei to observe rings of planets and their satellites.
It helped Galileo understand the motion of planets around the sun and establish the sun as the center of our solar system (Heliocentrism). As opposed to previously accepted Geocentrism where the Earth was believed to be the center of the solar system.
Earlier Refractor telescopes were plagued by massive aberrations mainly due to imperfect measurements and manufacturing limitations. Plus they were only available in small sizes as making a larger aperture lens was next to impossible.
To counter all these issues Issac Newton invented the reflecting telescope as an alternative to the refractor telescope.
The new design used mirrors instead of lenses. This was a big win as it was easier to make large accurate mirrors than a lens.
While the reflector telescope is more popular amongst amateur astronomers but there are people who absolutely love their refractor telescopes and consider it a superior telescope design.
Difference between Reflector and Refractor telescope (and their Advantages and disadvantages)
- Uses a mirror as its main objective
- Main objective (mirror) is present towards the back
- Mainly used for observing deep space – Galaxy, Nebula, and other Celestial bodies
- Economical – Large aperture at lower prices
- Invented by Issac Newton as an alternative to lens-based refractor telescopes (Also called – Newtonian telescope)
- Open tube – often collects dust and influenced by humidity
- Produces inverted images (upside down)
- Unlike refractors, it does not suffers from chromatic aberration
- Available in multiple designs
- Super lightweight compared refractors with similar dimensions
- Have Comatic (COMA) aberration
- Not ideal for daytime terrestrial usage
- Requires cleaning and maintenance
- Needs regular collimation (lens alining)
- Takes cooling time to acclimate itself to its surroundings
- Uses a lens as its main objective
- Main objective (lens) is present at the front
- Mainly used for observing planets and moon
- Can also be used for terrestrial observation (eg-bird watching)
- Better optical quality – Produces crisp and clear images
- One of the earliest telescope designs used by Galileo Galilei to observe planets and their moons
- Closed tube – protects against dust and humidity
- Low maintenance and no collimation required
- Requires low time to set up (Grab and Go)
- Rugged and strong with great build quality – lasts a long time
- Cheaper refractor telescopes suffer from chromatic aberration
- Needs additional lenses to correct for aberration (achromat, apochromat)
- Making lenses with a larger diameter is difficult
- Large Aperture refractors with Apocromats can get outrageously expensive
How does a Reflector and Refractor telescope work? (Explained)
All the similarities and differences mentioned above are the direct result of the differences in the internal design of the Reflector and refractor telescopes.
We all know a Reflector telescope uses mirrors and Refractors use lenses. But how these elements (lens and mirrors) are placed inside the optical tube of a telescope? and how do they bend light to form an image?
That is what we are going to learn in the next section.
Working of a Reflector telescope
A reflector telescope uses a single or combination of concave (bending inwards) mirrors to form magnified images of distant objects.
Reflector telescopes use a hollow tube through which the light hits the parabolic mirror placed at the base of the tube. The light then reflects and hits the secondary mirror placed at the center of the tube.
The secondary mirror points at 45°, which directs the light towards the eyepiece – where the image is finally formed.
Working of a Refractor telescope
The design of the refractor telescope has not changed much in the last couple hundred years. A basic refractor uses a primary objective (a convex lens) which is attached to the front of the scope, and a secondary lens located at the back.
When light enters the telescope, it interacts with the convex lens and bends inwards to meet at the focus which is then directed to our eyes by the eyepiece at the back to create a magnified image.
Optical quality and image formation in Reflector and Refractor
Reflector telescope – The amount of light collected by the telescope has a huge effect on what you can see through it.
Unline lenses, mirrors are cheaper and easier to make and can be easily made into larger 10, 12, 16 inches, or even larger sizes.
The telescope with a larger aperture collects more light which results in more information begin collected, ie. better resolution. It allows you to see fainter objects which are normally not visible in the night sky.
The images formed on these telescopes are inverted, which is not a big deal as these telescopes are mostly used for deep space observations where there is no up and down.
The biggest advantage of this Reflector telescope design is they do not have chromatic aberration, resulting in crisp images.
Refractor Telescope – Refractor telescopes are favored by astronomers for their superior optical quality.
As there is no secondary mirror blocking the optical pipe (like in reflector design), images from Refractor telescopes are sharp and contrasty.
This allows us to see the faint deep sky objects as well as planets like Mars, Jupiter, and the rings of Saturn.
The images produced by these telescopes are inverted (upside down) which can make it a little difficult to navigate the night sky.
However, in case you are planning to use this telescope for daytime (terrestrial) usage, you will need to erect the image the right way up using a diagonal. Most of the telescopes come with some kind of diagonal already included with the scope.
Ease of use and maintenance
Ease of use can be a big factor when looking for your first telescope. A telescope that takes a long time just to set it up can be a big enthusiasm killer for beginners.
The setup time also affects how often you will be able to use these telescopes. Ideally, as a beginner, you want something that is super quick to set up and doesn’t requires a lot of fiddling around.
Things like proper storage and maintenance also play an important role to ensure quick setup time.
Maintainance and ease of use – Reflector telescope
Since the reflector telescope is open from the top, they are prone to dust, humidity as well as temperature changes.
For the telescope to work properly and keep them functional for a long time, you need to regularly maintain (clean) them and protect them from elements.
The mirrors on the reflectors can also move ever so slightly while transportation or normal usage. This results in misalignment of the mirrors resulting in blurry images.
To fix that you need to realign the lens from time to time by a process called collimation. Collimation is easy to do but can be tricky for beginners and needs some practice to master it.
Mirrors on the Reflector telescopes are very sensitive. They are more easily affected by the difference in temperature inside and outside the tube.
Depending on the size, the Reflector telescope should be rested for 15 to 30 minutes to maintain an even temperature from the outside. This is what we call a cool-down period.
Transportation is another important factor, smaller telescopes are easier to carry from your house to a star party, but that can be difficult with larger/ wider telescopes.
Bigger reflectors need more protection as their overall construction is not as solid as refractors. Also, mirrors are easier to scratch, chip, damage, and break – compared to lenses.
Overall we can conclude that reflector telescopes require regular maintenance and need some time to set up before they are ready to use.
Maintainance and ease of use – Refractor telescope
Now since Refractors have a lens at the front and an eyepiece at the back, it forms a closed tube. Due to its closed tube design, the refractor telescopes are well protected from outer elements such as dust and humidity.
And thanks to their excellent construction where the lens firmly adhered to the body and the optics do not move, wobble and get out of alignment and hence these telescopes require almost no maintenance.
Their rugged construction also makes it easier to carry without risking damage.
Since the Refractor telescope has a closed tube, they do not often require any cool-down period (unless there is a huge temperature difference). That is why they are often called a grab-and-go telescope where all you have to do is – put them on a telescope mount and start observing.
Optical issues (Aberrations) in reflector and refractor telescopes
As we know, telescopes are sensitive instruments that require extreme precision.
Even slight deviation and inaccuracy in the mirror and lens can result in blurry views with heavy color fringing, which is obviously not good.
Some of the optical issues are inherent to the design and type of telescope, for example, Comatic aberration is common in cheaper Reflector telescopes. Whereas Chromatic aberration is common in aromatic Refractors.
These optical aberrations are more common in cheaper telescopes. More expensive telescopes use a combination of elements as well a higher quality optics to negate these issues.
(COMA) Comatic aberration in Reflector telescopes
While reflector does not have chromatic aberration but they do have Comatic aberration where the light meets together at the same focal plane but not on the same focal point. This results in comet-like starts, especially at the edge of the field of view.
This is more amplified on higher magnification. To fix this, you can get a COMA corrector lens.
Chromatic aberration in refractor telescopes
Lenses have the tendencies to react differently to different wavelengths (color) of light.
As the while light consist of different wavelengths – when it passes through the lens different colors of light meets at a different focal point.
For example, blue light bends more than red light and meets at a different point – this is what we call a chromatic aberration.
This issue has been plaguing refractor telescopes since the very beginning. At higher magnification looking through these telescopes, you would see color fringing around your target objects.
To fix the chromatic aberration telescopes come with stacked lenses that makes different wavelengths of light meet at the same focal point.
Types of Refractor telescope (based on lens stacking)
Refractor telescopes are available in three types depending on the number of lenses stacked together to form a primary objective.
- Single-lens – different colors meet at different focal points
- Achromat (doublet) – Red and Blue rays meet at the same point
- Apochromats (triplet) – All rays meet at the same point
Achromats – Most of the astronomical refractors telescope nowadays are achromat refractors with two lenses stacked together to form a primary objective.
They make two different colors (usually red and blue) to meet at the same focal point.
They greatly reduce color fringing but you can see still experience a purple halo around bright small objects such as stars.
Apochromats – For bringing the third color (usually green) to the focal point we introduce the third correcting lens.
Apochromats are telescope with three lenses stacked together to form a primary objective. They allow all three colors namely – red, green, and blue to meet at the same focal point resulting in the best optical quality.
The Apochromatic telescope produces the brightest and sharpest views of the night sky with excellent contrast.
But on the flip side, these telescopes are very expensive. Even a medium-sized 4 or 6-inch Apochromat Refractor can easily cost two or three times more than their mirror-based counterparts.
Apochromats are an excellent choice for capturing faint objects such as galaxy or nebulae or to look a the moon and nearby planets.
Common sizes of telescopes for beginners
In the telescope world – how much light a given telescope can collect is more important than the length of the tube or their zooming capabilities.
That is why telescopes are measured in terms of their diameter (ie. Aperture). The larger the Aperture, the more light a telescope can collect – resulting in superior views of the night sky.
Common sizes of Refractor telescope
Refractor telescopes vary greatly in size as they use mirrors which are cheaper to make and easier to scale.
Most people would agree that 4 to 6 inches are a great size for a beginner Reflector telescope.
But if you want to step up your game an 8 or 10-inch telescope could be a good choice for intermediate to hardcore astronomers.
An 8-inch Reflector (like this one) is a great size as they provide excellent views of the night sky. They are very flexible and can be used for viewing near as well as distant objects.
Common sizes of Refractor telescope
The sizes of the refractor telescope are limited by its aperture. While 3 and 4-inch refractors are fairly common but anything beyond that gets crazy expensive especially if it is an Apochromat refractor (triplet).
While there is no official measurement of telescope sizes, still refractor telescopes can be roughly classified as follows
- 60 ~ 90mm Aperture – Small refractors
- 100 ~ 120mm Aperture – Bigger refractors
- 120 ~ 180mm Aperture – Heavy monster refractors
Keep in mind that there is an upper limit for the size of the lens – as they start to bend and break under their own weight.
Catadioptric Telescope (Lenses + Mirrors)
One of the most common issues in Refractor telescopes is they produce views with distorted colors. And when you buy an Apochromat Refractor telescope with no color distortion issues – it costs too much (way out of a beginner’s budget).
Similarly, Reflector telescopes suffer from Coma aberration, where the stars near the edge of the field of view appear to have a comet-like tail, which is not a good look.
Catadioptric telescopes are a hybrid design that incorporates both mirror and lens elements into their design to produce a more refined optical path with minimum aberrations.
This results in a near-perfect view of the night sky with no color distortions and Coma issues, especially at the corners of the field of view.
Schmidt-Cassegrain telescope (SCT) is the most popular Catadioptric telescope design.
Its SCT design consists of a concave mirror as a primary objective located at the base of the optical tube, a full-aperture corrector lens located at the front, and a secondary mirror (convex) placed at the center of the optical path.
The light reflects from the secondary mirror and passes through the hole at the center of the main objective to finally form the image. The image is formed behind the primary mirror.
Advantages of Schmidt Cassegrain telescopes
- The bottom positioning of the eyepiece makes it very convenient to use while physically observing the sky as well as astrophotography
- The use of multiple mirrors results in a folded path, that reduces the length and mass of the telescope
- SCTs are easier to transport
- Fairly strong and sturdy
- Due to their compact design SCT are easy to balance on the telescope mount
- Talking of mounts, these Schmidt Cassegrain telescopes are available in all types of mounting options, including the fully automatic star-aligning mount
- Reasonable price (Advance telescope with great capabilities at good price tag)
- Requires more frequent optical alignment, compared to Reflectors.
- More complex parts
- Can easily get heavy with an increase in Aperture
All these great advantages, as well as a relatively cheaper price tag, have made the Schmidt-Cassegrain telescope (SCT) a very popular choice amongst both beginners as well as experienced astronomers.
If you are just beginning, getting a hassle-free automatic version of the SCT telescope is a great alternative to Reflector and Refractor telescope.
The Schmidt Cassegrain telescope is available in multiple apertures. For beginners, we recommend SCT with 4 or 6 inches of Aperture. For more experienced astronomers an 8-inch SCT is a good option.
Reflector or Refractor or Catadioptric: Which telescope should I get?
When it comes to buying a telescope, some of you may say – We should get a telescope with the best optical design.
The only problem is – “There is no such thing as a superior telescope, every optical design is always a compromise”.
No single telescope is going to be the perfect telescope for every application or for every budget.
So how do you pick the right telescope for yourself?
There are several factors that need to be considered when selecting a telescope for yourself. The first and foremost is what do you want to look at. Is it the moon, the planets, or deep space objects?
Also, how experienced an observer you are. Based on that you can decide between an easy to set up a telescope or a fully automatic computer-controlled telescope.
Once you finish observing, you also need to consider – how much space do you have for storage? How much weight do you want to carry?
And finally, the most important factor is your budget. If you are on a low budget, you should naturally look for a telescope that gives you the largest aperture size. In case you have decent money, then you can look into the quality of optics and some advanced design/ features.
Beginner (entry-level) telescope – 70 to 100 mm Refractors
If you are a beginner or looking to buy a telescope for your young ones, getting a 70-100 mm refractor telescope is a very good option.
These are some of the best entry-level telescopes that provide a wide range of viewing options at the cheapest possible price.
This telescope can give you a great view of the moon and nearby planets plus they re also a good option for daytime terrestrial viewing.
Out of all entry-level refractor telescopes in the market, we found that Gskyer 70 mm Astronomical Refractor telescope is the best choice for beginners.
Despite its relatively low price, the optics used in this telescope is good, plus it comes with a number of accessories such as an adjustable tripod, a finder scope, multiple Barlow lens and eyepieces (10mm and 25mm), a smartphone adapter, a wireless remote as well as a travel bag.
Budget telescope – 4 to 5-inch Reflectors
If you are low on budget but still want some powerful equipment to kickstart your astronomy journey a reflector telescope with 4-inch aperture is a good choice.
These telescopes provide a great view of the moon as well as powerful enough to see brighter nebulas such as Orion.
The Orion Starblast 4.5 Dobsonian reflector telescope and Orion Starblast 4.5 equatorial reflector telescope are the two scopes that we recommend. Both these telescope comes with a 4.5-inch mirror with a lower f ration of f/4.
Due to their smaller-compact size these telescopes are very lightweight and easy to set up and they kind of feels like a grab and go telescope.
The 4.5-inch mirror gives a great view of the moon and their shorter focal length gives a wider field of view which is suitable for observing nebulas and galaxies.
Intermediate level telescope – larger 6/ 8 inch Reflector or SMT
A 6 or 8-inch Reflector or SMT are seriously some of the best value-for-money telescopes in the market.
This aperture gives you a lot of flexibility. You can get an up-close look of the distant planets with easily discernable patterns of Jupiter and the rings of Saturn.
These larger apertures are also great for faint deep space objects and produce some incredible results.
On the cheaper side, you can get the Orion Starblast 6i Dobsonian telescope with a computerized object locator. On the expensive side, you can get the very popular Celestron NexStar series of SCT (Schmidt-Cassegrain telescope) telescope.
Anything above 8 inches is kind of an overkill for a beginner.
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