Last updated: August 10, 2021

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A telescope allows you to explore distant objects. A distinction is made between two types of telescope in terms of their purpose. There is the astronomical telescope and the terrestrial telescope, better known under the terms telescope and monocular. The telescope is mainly used for observing the sky, so you can explore planets, moons and constellations.

The monocular, on the other hand, is suitable for use on earth, with which you can observe animals in the wilderness or explore unique landscapes. With our big telescope test 2021 we want to help you find the right telescope for your project.

We have analysed and compared terrestrial and astronomical telescopes for you. We found the advantages and disadvantages of the models and have summarised them for you in this article. We want to support you in your purchase decision so that you can find your perfect telescope.




Summary

  • The telescope is an optical instrument that allows you to observe distant objects in a magnified way. If you want to observe objects on Earth, a terrestrial telescope is the right choice for you. For observing the sky, you should buy an astronomical telescope.
  • The magnification of your telescope depends on the size of the objective and the diameter of the eyepiece. The more light your telescope can capture, the better the images will be with the right eyepiece.
  • You can use your telescope, whether it's a monocular or a telescope, for more than just observing. With a special smartphone adapter, you can also take great pictures of planets or wildlife.

The Best Telescope: Our Picks

Guide: Questions you should ask yourself before buying a telescope

What is a telescope?

A telescope is an optical device that allows you to look at distant objects in a magnified way. The telescope allows you to see magnified and sharp images of distant objects, such as planets or animals.

How many types of telescope are there?

There are refracting telescopes and reflecting telescopes as supercategories. Regardless of which category they belong to, telescopes are distinguished in terms of their use. Thus, there are astronomical telescopes and terrestrial telescopes. Astronomical telescopes, as the name suggests, are suitable for observing celestial bodies. Terrestrial telescopes are suitable for observing objects on earth, as they do not display everything upside down like astronomical telescopes due to a reversing lens.

The best-known type of telescope is the refracting telescope

The best-known terrestrial and astronomical telescope belongs to the lens telescope genus. Lens telescopes are also the most frequently produced and sold. For this reason, this section deals specifically with this type of telescope. The most famous astronomical telescope is clearly the Kepler telescope. It was invented by the German mathematician Johannes Kepler and has a sharp image quality.

It consists of a long focal length objective and a short focal length eyepiece. As already mentioned, the astronomical Kepler telescope shows a mirror-inverted image and is therefore useless for Earth observation. Most people know the astronomical Kepler telescope as a telescope. The most famous terrestrial telescope is the Dutch telescope. It was developed by the Dutchman Jansen Zacharias and optimised a few years later by another Dutchman, Heinz Lippershey.

It also consists of a long focal length objective and a short focal length eyepiece. However, there is a converging lens between the objective and the eyepiece that inverts the image. This produces an upright image. The Dutch telescope is in principle a pair of binoculars, but in its single version it is known as a monocular. You can find out how the telescope works in detail in the following section.

How does a telescope work?

All refracting telescopes work on the same principle: two light rays from the observed object are captured by the lens and bundled in the lens to form a real intermediate image. This real intermediate image again sends rays to the eyepiece, this eyepiece acts like a magnifying glass on the rays.

These magnified rays from the eyepiece are passed on to the eye and there bundled and passed on to the retina. From the retina, the rays reach the brain via the optic nerve. However, the brain always assumes that light is emitted in a straight line. Thus our brain creates a virtual image in a rectilinear extension, this virtual image is displayed to us greatly magnified.

Here is a short video for you to help you understand how it works. Whether the image is displayed upside down or not depends on whether a converging lens is installed between the lens and the eyepiece. If there is a converging lens, it reverses the intermediate image and it is displayed upright. Thus, the difference between an astronomical telescope and a terrestrial telescope lies in the installation of the converging lens.

How far can you look with a telescope?

The quality of the magnified image always depends on the diameter of the objective lens. This means that the larger the objective, the more light falls in and the better the image can be magnified. However, in order to view the image, you also need an eyepiece. This eyepiece also plays an important role in the topic of maximum magnification. Theoretically, there is no limit to how far you can look.

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You can observe the night sky wonderfully with a Kepler telescope.
(Image source: 123rf.com/ Sadovski)

You can calculate the maximum magnification of a telescope with a simple formula. You take the focal length of the objective and divide it by the focal length of the eyepiece. You can find all the information in the sales description, especially for astronomical telescopes, where the maximum magnification is also listed in most cases.

Now back to our formula, which allows you to easily check whether everything in the description is correct. Here is a small calculation example for clarification: If you use a telescope with a focal length of 600mm and an eyepiece with a focal length of 5mm, then you divide the focal length of the lens by the focal length of the eyepiece, so you calculate 600/5=120.

The result 120 means that you can achieve 120x magnification with this telescope.

On average, the magnification of commercially available telescopes is between 150 and 400, but this value varies greatly depending on the eyepiece supplied. So it is best to always read the product description. In the case of terrestrial telescopes, also called monoculars, there is often no information about the eyepiece in the sales description.

Here you will only find descriptions such as 10x25. If you can read these numbers, it is easy to determine the maximum magnification of the product. The front number in our example, 10, is the maximum magnification and the back number here, 25, is the lens diameter. Thus, a monocular with these figures can magnify an object 10 times.

Which telescope for which activity?

As the name suggests, you use an astronomical telescope primarily to observe objects in space. These can be moons, stars, asteroids and various planets. Observing the moon is particularly exciting, as it is the brightest and largest object in the night sky.

A telescope is a wonderful way to observe distant planets and stars

The moon itself does not emit its own light, but is illuminated by the sun and reflects the light. The telescope is also a wonderful way to observe the different phases of the moon, such as full moon and half moon. Observing distant planets is also possible with a Kepler telescope. Like the moon, the planets do not emit their own light, but are illuminated by the sun. This light is very bright, so you can see the planets well even in the ambient light of a large city. If the night is very clear and you are lucky, you can even see details of the planets, such as Saturn's rings.

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A telescope is also an excellent way to explore the signs of the zodiac.
( Image source: 123rf.com/ Kotoffei )

The monocular, on the other hand, is suitable for activities on Earth. Whether you use it for professional purposes like hunting or as equipment for various hobbies, it makes no difference. A good telescope can give you great magnifications of animals, landscapes and other objects. Monoculars are ideal for outdoor activities because they are small and compact, especially when compared to bulky binoculars.

A handy monocular gives you the opportunity to observe animals from a long distance without scaring them away. Since there are many telescopes of this type in different designs, waterproof ones are also available. This is useful if you get caught in a rain shower. If you are out at night, there are also many monoculars with night vision function.

This gives you the best possible view even in the dark. The night vision function is especially interesting for hunters who want to scout an area for game. But it can also be an advantage for adventurers who like to hike; on a night hike you can always keep an eye out for interesting events.

What does a telescope cost?

Depending on whether you want to buy an astronomical telescope or a terrestrial one, the prices differ greatly. Of course, the price also influences the magnification quality of the respective telescope; with a more expensive telescope you will get better pictures. For a Kepler telescope, the price range is approximately 80-1000 pounds. As you can see, there is a lot of room for manoeuvre.

The prices for monoculars are much lower, but there are also expensive versions. You can buy inexpensive models for as little as 8 pounds, but there are also more expensive models for a whopping 350 pounds. Here, too, there is an enormous price difference between the different models.

Type of telescope price range
Telescope 80-1000 pounds
Monocular 10-350 pounds

Whether you should buy an expensive telescope or a cheap one depends on how often you use it and what you intend to do with it. As a hobby astronomer who wants to observe the stars at the weekend, a telescope for 80-150 pounds is sufficient. But if you want to work with it and use it for study purposes, a larger investment is worthwhile for better results.

It's the same with monoculars, if you're going hunting, an expensive telescope would be an advantage. This way you can look further and keep an eye on things at night if necessary. However, if you go hiking from time to time and want to observe nature and birds, then you can also choose a cheaper version.

Decision: What types of telescopes are there and which one is right for you?

If you want to buy a telescope, there are two types you can choose, depending on what you want to do:

  • Astronomical telescope
  • Terrestrial telescope (monocular)

Depending on what you want to explore with your telescope, you can choose between a telescope and a monocular. If you want to observe objects in space, then the astronomical telescope is the right choice for you. But if you want to observe animals or similar things here on earth, then the terrestrial telescope is suitable for you.

Of course, the two telescopes not only serve different purposes, but also need to be maintained, adjusted and used differently. Also, depending on the telescope and the planned activity, you will be in a different price segment. In the following section you will learn more about the advantages and disadvantages of each telescope.

What distinguishes a telescope and what are its advantages and disadvantages?

The big advantage of a telescope is that you get really great views of the universe. It is possible to see distant planets with details and entire star images. Good entry-level models are often sufficient for this. Whether young or old, images from space are fascinating for everyone.

A telescope can be especially beneficial for children, it teaches them that natural sciences are exciting and interesting. The Kepler telescope is available in different lengths and sizes. Also, a tripod is always needed for use, as you have to align the telescope correctly to see anything.

Advantages
  • Bright instrument
  • Low shading
  • Large field of view
Disadvantages
  • Difficult to handle due to long design
  • Often very heavy
  • Storage and maintenance costly

Since a refracting telescope is much cheaper to manufacture than a reflecting telescope, you can explore space for a reasonable price. A Kepler telescope is a sensible investment for such an activity, but you need to be aware of how intensively you want to observe. If you have more ambitious goals, you will have to dig deeper into your pockets.

You also need to learn how to use the telescope; adjustment and alignment play a major role in your discoveries. Many manufacturers often include an astronomy manual with their products. If you are completely new to the subject, you should look for this in the product description.

There are not only things to consider when adjusting and aligning your telescope, but also when storing and caring for it. You need to protect your astronomical telescope from external influences such as heat and moisture, otherwise mechanical damage or limitations in the optics may occur.

What are the features of a monocular and what are its advantages and disadvantages?

A monocular gives you the advantage of being able to view magnified images of distant objects. Whether you use it while hiking or at a big concert to look at the stage, it doesn't matter. However, you have to be more careful when buying a monocular, because not every monocular is suitable for outdoor use.

Depending on what you want to do, you should also pay attention to the maximum magnification. You will most likely only be able to observe shy birds with a somewhat more expensive telescope.

Advantages
  • Perfect for earth observation
  • Lightweight
  • Easy to adjust
  • Inexpensive
Disadvantages
  • Light losses occur due to reversing lens
  • Not all devices suitable for outdoor use
  • No spatial vision

Compared to binoculars, monoculars are much more practical and handy. They are also easy to operate and you can use them for hunting or nature observation. Unlike astronomical telescopes, you don't need time-consuming alignment and adjustment. For occasional use of a terrestrial telescope, you don't have to spend too much money.

However, if you need it for professional purposes, a monocular with night vision function can cost several hundred pounds. You also have to make sure that it is waterproof, as many models are only built for indoor use.

As the name of the monocular suggests, you only use one eye. This means that, compared to binoculars, you do not have spatial vision. When observing objects, you lack depth perception, which can make it difficult for you to judge distances correctly.

Buying criteria: These are the factors you can use to compare and evaluate a telescope

In the following, we will show you which aspects you can use to decide between the many different telescopes. The criteria you can use to compare telescopes include:

Magnification

The quality of the images you get through a telescope depends on the magnification capability of your instrument. The longer the focal length of your objective and eyepiece, the better your telescope or monocular can magnify images. This is because more light enters the body of the telescope.

  1. Telescope magnification range: The range of magnification for commercially available telescopes is between 150 and 1000. Of course, the better the telescope can magnify, the higher the cost. Therefore, it is important for you to choose a telescope with the appropriate magnification for your project.
  2. Recommended magnification: For good images in the hobby area, magnifications in the range between 200 and 400 are sufficient. This also keeps the costs manageable. If you use the telescope more intensively, it should be capable of a magnification of 600 and upwards.
  3. Magnification range monocular: The same principle applies to monoculars, the better your telescope can magnify, the further you can see. The magnification range here is between 6-40.
  4. Recommended magnification: If you intend to observe wildlife from a safe distance, you should buy a monocular with a magnification of at least 10.

Field of view

In addition to the magnification capability of the telescope, the field of view is also important. The field of view describes the distance in metres from the left to the right edge of the eyepiece at a distance of 1000 metres. This means how many metres of horizontal field of view you have in one kilometre.

A wider field of view makes it easier for you to find your way around. With a telescope, the field of view can affect your viewing pleasure. With a larger field of view, you can observe more easily and comfortably, and you can also see small details around the planet. If the field of view is small, you can only see the planet in your eyepiece, for example.

Details or the surroundings around the planet no longer fit into the field of view. If you spend more time at the telescope, then a larger field of view is suitable, as it is more comfortable for the eye in the long run. Similarly, if you are using a terrestrial telescope, a wide field of view can help you keep a better overview.

Especially in situations where you need to act quickly, this can be an advantage because you already have the surroundings in your head. Of course, telescopes with a wider field of view are more expensive.

Waterproofness

Since astronomical telescopes can only be used in good weather, i.e. clear night skies and good weather, the question of waterproofness answers itself. A telescope is not made for use in the rain, so it is not protected against it.

Even if you store your telescope on the balcony, it should always be covered. If you want to buy a monocular for outdoor use, then you should make sure in the product description that it is waterproof. Waterproof monoculars often have a slightly thicker rubber coating around the housing.

This is to protect against the weather. Waterproof monoculars are available for as little as 10 pounds. You don't necessarily have to buy an expensive monocular just because you are looking for a model for outdoor use.

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You can also use a waterproof monocular on a rainy hike.
( Photo source: 123rf.com/Kuznetcova)

Weight

The weight of telescopes is strongly dependent on their size, logically a larger and longer telescope is a lot heavier than a lighter one. Commercially available telescopes weigh between 2 and 25 kilograms. You can see better images with the heavier telescopes because their size allows them to capture more light.

However, you will have a much harder time adjusting and aligning them. This could be a problem if you don't have much strength or if you want your children to use the telescope. Especially in the latter case, you should rather look for a lighter telescope, as there are some that allow great images despite their relatively low weight.

The weight range for monoculars is between 100 and 500 grams. Heavier monoculars are often larger and have a larger objective lens. If you have to hold the telescope in your hand for a long time, e.g. when birdwatching, then a not too heavy version is worthwhile.

Type of telescope weight
Telescope 2-25kg
Monocular 100-500gr

Twilight figure

If you want to buy an astronomical telescope, the twilight number is not interesting for you. The twilight number tells us how well a telescope can see details in low light conditions. This is because in low light, smaller objects tend to be easily recognisable - larger objects with a small surface area, such as a comet tail, are only really perceived by the eye when the entire retina is used and not just a part of it.

For low-light observations in space, the exit pupil is a better value. With monoculars, on the other hand, the twilight factor is a reliable value for determining the telescope's capabilities in poor light. Good values here are between 12 and 25.

Eyepiece magnification with eyepieces included

As mentioned earlier, the exit pupil is a better value for observing in space than the twilight factor. The exit pupil tells you how large or small the magnification is. The larger the value of the exit pupil, the smaller the magnification and vice versa. You are probably wondering what the exit pupil has to do with the eyepiece.

Well, the value of the exit pupil depends on the size of your eyepiece. In the calculation example above, you can see what influence the eyepiece has on the magnification. So if you want to make good observations, you should look in the product description at the eyepieces supplied and their values. This will tell you how useful your telescope will be.

Mounts

Whether it is a telescope or a monocular, the mount is very important for its use. Especially with a telescope, a stable tripod is indispensable. Only then can you align it perfectly and enjoy a pleasant viewing experience. The tripod should not wobble and should be non-slip so that your telescope does not come to any harm.

Good monoculars often have integrated hand straps so that you can hold them comfortably in your hand. This has the advantage that you have a firmer grip and get wobble-free images. Since most telescopes are covered with rubber, the hand strap is very practical. This way you don't get sweaty hands despite the rubber coating of the monocular.

The best way to find out whether the mount is suitable for use is to read the reviews of the respective product. Here you can find out from many buyers how well you can work with the device.

Facts worth knowing about telescopes

How do I adjust a telescope correctly?

The most popular mount is the parallactic mount, where the telescope sits on two axes, one of which is aligned parallel to the Earth's axis. This means you only have to turn one axis to keep an eye on the stars.

1. Pre-adjustment: The first thing you need to do is to preadjust the scale on the side of the telescope to the altitude of your location. This is done by tightening the altitude screws. Before you do this, of course, you must determine the latitude of your region.

2. Taring: After the presetting, you still have to tare your telescope so that no axis is overloaded in a certain direction. First open the right ascension axis, which will later become your tracking axis. Now you can hold the axle on the counterweight rod and check whether the axle is overweight in one direction.

Then open the screw for the counterweight, move the weight a little and test again if the axle is warped. Do the same process with the declination axis, again opening it and checking if the tube falls in one direction. If it does, open the clamps and carefully slide the tube up and down until it is stable.

3. Adjust the scope: Once you have adjusted the axes correctly, you only need to adjust the scope correctly. To do this, find a high object far away, such as a power pole or church tower. Then move the telescope with the preset axes in the direction of the object. Now you can look through the small scope and move the telescope until the object is in the centre of the crosshairs.

After the whole procedure, your telescope is ready for use and you can put the eyepiece into the focuser. The parallactic mount is explained in more detail here. With a monocular, the adjustment is much easier, because in most cases you don't have a frame. Take the monocular in your hand, close one eye and look through it. Use the wheel on the side to adjust the zoom.

What do I need to connect my smartphone to the telescope?

To connect your smartphone to your Kepler telescope, you need a smartphone adapter. This can be compared to a mobile phone holder for your car. You mount the smartphone adapter on your telescope and the mobile phone camera rests on the eyepiece. In this way, it records everything that your eye would actually see.

Through the shutter release you can now take wonderful photos of your observations, so you have great pictures that you can share with your friends. Such adapters are usually not expensive, you just have to make sure that the width of your smartphone is compatible with the adapter.

Such adapters also exist for monoculars. Of course, they are designed differently because a monocular is much smaller than a telescope. However, the concept is identical, and again you have to take into account the size of your smartphone.

How do I use the telescope correctly?

If you have already adjusted your telescope correctly, you have the basis for correct use. It is important to be careful with the two devices, as they are technical devices and can quickly break. The monocular is of course more robust and can withstand more, as it is much smaller and more compact. Whether you use a terrestrial or astronomical telescope, you should never look directly at the sun.

This can damage your retina, and in the worst case you could go blind. A telescope is only used at night and when the sky is clear. For daytime observation, you can buy special sun filters. These filters should always be attached to the lens. Never attach these filters to the eyepiece, as they can burn there. Even if you use the filters, you should never look at the sun.

How do I care for a telescope properly?

Telescopes for Earth observation have to withstand a lot, as they are used outdoors all day. To ensure that you can use your monocular well despite various weather conditions, you should take good care of it. Dirt residues on the lens can be removed with lens cleaner. You can buy this on the Internet or in specialist shops, and a microfibre cloth is best suited for cleaning.

Minor dirt in the gaps and on the edges of the telescope can easily be removed with a brush. To care for your telescope, you will need a lot more utensils. The most important are isopropyl alcohol, a dosing bottle, microfibre cloths, an air pump and talcum powder. Let's start with the eyecup, which protects the eye from stray light. Here you can simply take some talcum powder and rub it into the eyecup.

This keeps the rubber soft and prevents it from becoming brittle. Dust on the lens can be removed with an air pump. For streak-free cleaning of grease residues, fill a bottle with isopropanol and wipe over with a microfibre cloth. You can also use it to clean the lenses inside the telescope.

Image source: sorax/ 123rf.com

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