New to the world of astronomy? Got surprised by the different types of telescopes? It's not something unusual. When you think about a telescope for the first time, you might imagine a scope shape with a long glass lens at one end through which the light passes. Yes, it exists. But there are more types to know, just a few points to keep in mind. And then getting introduced to each scope type separately will be easier for you.
For your better understanding, we arranged this guide with the basic types of telescopes and their specifications. Get a clear idea of what telescope you prefer most, why you should consider one scope over another.
- Types of Telescopes
- 1. Refracting Telescope
- 2. Reflecting Telescope
- 3. Catadioptric or Compound Telescope
Types of Telescopes
In each telescope there is a part that gathers the light into the image and this part is known as objective. The given three telescopes are classified according to their objectives. You might hear more terms of telescope types but they are actually the variants of those basic three. Thinking of the basic telescopes? What do the terms mean? How do they work? Well, stay with us and get the answers to your queries.
1. Refracting Telescope
When it comes to a refracting telescope, the first thing that may appear in your mind, “What's a refracting telescope?”
Refracting telescope is an optical instrument that uses specifically designed lenses to bend the light into the focus. Thus an image of a distant object comes to be visible. That means, the objective of a refractor is its lenses and this objective makes it different from the other scopes.
Structure of refractors
Refractors are smaller, more lightweight, and portable than other telescopes. But still, they are long relative to their sizes as they need to be. You know why? Let us explain. There are two lenses (an objective and an eyepiece) in a refractor. The first lens is at the end of the tube. The second one or the eyepiece is at another side. These two lenses are designed in a convex shape and that's why they are called convex lenses.
While observing through a refractor, the light that comes from an object needs to flow in a straight way through the optical tube and reach the eyepiece. If it can't flow directly, it might not go to the eyepiece where you keep your eyes. As a result, you can't observe the object. The larger the lens, the longer the tube needs to be. Otherwise, it can't bring the images into focus.
How a refractor works
You have already known that retractors use lenses to gather light. Now the question is, “how do they work?” Let's know.
- First, the light comes from a targeted object and refracts on the first lens of the tube.
- Then the light straightly passes through the tube and goes to the secondary lens or the eyepiece.
- The primary lens works to gather light as much as possible and the secondary or the eyepiece does the magnification.
- Thus an image comes into focus and becomes visible to you through a refractor.
- As the magnification occurs in the eyepiece, you can change it according to your demand whether you want less power or need maximum power.
Example of refractors
You have probably heard of doublet or triplet telescopes. They are actually the variants of refractors. And basically, these two terms reveal the numbers of lenses of the objective. Let me guess what you are thinking now. You are wondering what these two refractors mean, right? Okay, let's explain.
A doublet uses two lenses to focus on the object. It is also known as achromatic lens or achromat. This achromatic lens is used to bend two wavelengths into focus according to the same direction.
Purpose of a refractor telescope
The purpose of a refractor telescope is to make the celestial objects brighter by refracting with the help of lenses. They bend the light together so that an astronomer can enjoy a clear and magnified view in no time and can carry the refractors anywhere they want to observe.
Advantage & Disadvantage
- Transportable and lightweight
- Not necessary to clean or manipulate
- Incredible sharpness with great contrast
- No chance to be dirty as the tube is closed
- Not enough light collected
Things to consider
There are some specific things to keep in mind when it comes to a refractor.
- You might face a color fringing situation while observing through a refractor. Wondering what this is and why? Color fringing occurs when different wavelengths arrive at various angles for getting split from each other. At this stage, it shows an image with distinct coloration at the side.
- Basically, this is called Chromatic aberration and occurs in high magnification depending on the types of lenses you are using.
- If you use a doublet refractor at a low cost, you will probably face this problem. But a triplet refractor is designed to solve the issue.
- So you should consider whether you will use a doublet or a triplet. Except for the chromatic aberration, in both cases, you will find a refractor solid and easy to use.
2. Reflecting Telescope
A reflector is an optical telescope scientifically designed by mirrors where lights are reflected at various angles through the optical tube. You have already realized that a refractor uses lenses whereas a reflector uses mirrors to reflect the light into focus. And as the large mirrors are cheaper to manufacture than the large lenses, reflectors are relatively less expensive. The structure and focusing method of a reflector are different from a refractor.
Structure and working method
A reflector telescope is shorter than a refractor one. Because here the light doesn't need to pass in a straight way to move the same distance.
In a reflector telescope, the light coming from a distant object directly goes through the optical tube. Then the first reflection occurs on the primary mirror located at the bottom of the tube. The major part of a reflector is the primary mirror. Then it passes the light towards the eyepiece in which we keep our eyes. There is a secondary mirror located near the top of the optical tube. This mirror reflects the light for the second time and makes the object visual to the observers.
How do you focus on a reflector?
The focusing method in a reflecting telescope isn't something difficult. You can easily do it yourself. Follow the steps given below:
- First, rotate the focus knob slowly.
- Continue rotating until the object you targeted becomes focused.
- Move just a little bit beyond the sharp focus and switch the direction.
- When you will get a sharp focus, tighten the focus knob until it is locked.
- If you don't lock it, your focus may slip. So don't skip the step.
- When you are ready to refocus on a new object, loosen the focus lock knob again.
- The focus lock knob should also be turned while changing your eyepieces.
- Try frequently and the focusing will be easier for you.
Example of reflectors
Like the refractors, there are also different types of reflector telescopes. We just picked two types among them as an example.
The Newtonian telescope is an optical instrument that uses two mirrors to reflect the light. The first one is the primary or the concave mirror and the latter one is the secondary mirror. The Newtonian telescope is named after the name of Sir Isaac Newton as he invented it.
A Dobsonian telescope is also a reflector telescope using an altazimuth mount. John Dobson, an American astronomer first designed it and that's why it's named after him. Dobsonian is mainly a type of mount that is used for telescopes. And the telescopes using these mounts are called Dobsonian telescopes.
Purpose of a reflector telescope
The first purpose of a reflector telescope is to monitor the area of the electromagnetic spectrum that is visible. The second one is to find out all the wavelengths adjacent to it. And the final purpose is to make the distant objects brighter by reflecting.
Advantage & Disadvantage
- Gives the best view with a larger screen
- Relatively cheaper
- Easy building procedure
- The wavelengths reflect on the mirror in the same way and that's why chromatic aberration doesn't occur.
- Collimation procedure seems to be a little hard
- Mirror cleaning requirement
Things to remember
Though a reflector telescope is available at a reasonable price and gathers more light, yet you should remember a few things before using a reflector telescope.
- To adjust the alignment, collimation needs to be done before every observation.
- To collect a large amount of light, clean the mirrors frequently.
- The larger the mirrors, the brighter the objects. So choose the large mirrors for your reflector.
3. Catadioptric or Compound Telescope
The most interesting fact is that the catadioptric telescopes combine both the lenses and the mirrors to get the optical benefits. Basically, these hybrid telescopes are the mix of refractor and reflector qualities in their structure. And this convenient design made them easier to carry.
Structure & working method
You have just got that the catadioptric telescopes are designed like the reflectors or refractors as they use both lenses and mirrors. But along with the refractive optics and the reflective optics, there is a corrector plate at the front of the telescope that folds the light paths. And the secondary or the curved mirror reflects the light.
How does a catadioptric telescope work?
In a catadioptric, the incoming light that produces from a distant object goes through the corrector plate. Then the primary mirror reflects it into focus. And the light passes towards the secondary mirror where it is reflected for the second time. Finally, after the second reflection, the light comes back to the primary mirror through the tube. And there located an eyepiece that works to make the object visual to your eyes.
How do you focus on a catadioptric telescope?
Though the focusing method is exactly not the same as a refractor or reflector, it's not much different. Just a little difference here, let's see.
- First, find out the focusing knob on a catadioptric. If you get a small knob on the back of it, you are at the focusing knob.
- Here you don't have to move your eyepiece back and forth against the telescope.
- You just need to move the primary mirror backward and forward.
- By doing this, you can have a long throw of focus.
- And one more thing, now it's ready to accept any kind of various cameras or eyepieces
Example of catadioptric telescopes
Though a lot of catadioptric telescopes there, two majors are mostly known and available. Maksutov-Cassegrain and Schmidt-Cassegrain.
Maksutov-Cassegrain is one kind of catadioptric or compound telescope that uses a spherical mirror to gather light and a curved lens to protect the observation from chromatic aberration. It's also known as Mak-Cass or Mak. For the spherical design, Mak-Cass offers the spherically symmetrical convenience.
A catadioptric telescope using a folded light path is called a Schmidt-Cassegrain telescope. This compound telescope uses both mirrors and lenses to bring the light into focus. And they are specifically designed to reduce the optical aberration.
Purpose of a catadioptric telescope
The purpose of a catadioptric telescope is to make the infinite distant objects visible by focusing an amount of light and producing sharp and detailed images. They also reduce chromatic aberration using specifically shaped reflective and refractive optics.
Advantage & Disadvantage
- Shorter and lightweight
- Easy to transport for their mechanical size
- Low manufacturing cost
- Reduces optical aberration
- Frequent collimation is required to be done
- Long cool-down time
- A slight loss of light for using the secondary mirror
Things to remember
You have completely realized what a refractor, reflector, or catadioptric telescope means and how they work with different designs. You might have specific needs and your needs can make one telescope type more appropriate for you than another. Now probably you have curiosity in your mind, “Which telescope should you use when?” Let's see at a glance:
- If you are looking for a larger scope at an affordable price, you will probably love a refractor telescope.
- To have transport convenience and easy carriage, refractors can be the ideal choice.
- If you just want to watch the moon or any other nearby planets, use a small scope or a basic refractor.
- But to observe the sky deeply and watch the distant celestial objects, you may like to consider a reflector telescope.
- If your desire is to have a high degree of flexibility with brighter images, then any of the catadioptric telescopes will be a great value.
Considering the types of scopes and their features, advantages, disadvantages, you can easily select any type for you and have the most enjoyable viewing experience out of the night sky. Now if you have any queries or anything to know more, feel free to comment here. Leave your questions and share your opinions. We would love to help you out.