Home » Orthopedics » Telescope purpose device operating principle. How are telescopes of various optical schemes constructed? What types of telescopes are there?

Telescope purpose device operating principle. How are telescopes of various optical schemes constructed? What types of telescopes are there?

Imagine a human eye with a diameter of 5 cm. At the same time, it extends half a meter from the pupil to the retina. This is roughly how a telescope works. It works like a big one eyeball. Our eye is essentially a large lens. He does not see the objects themselves, but catches the light reflected from them (that is why in complete darkness we see nothing). Light enters the retina through the lens, impulses are transmitted to the brain, and the brain forms a picture. A telescope has a lens much larger than our lens. Therefore, it collects light from distant objects that the eye simply cannot catch.

The principle of operation of all telescopes is the same, but the structure is different.

The first type of telescopes is refractors

The simplest version of the refractor is a tube with biconvex tubes inserted into both ends - like this () – lenses. They collect light from celestial objects, refract and focus - and in the eyepiece we see an image.

Levenhuk Strike 80 NG Refractor Telescope:

The second type of telescopes is reflectors

Reflectors do not refract, but reflect rays. The simplest reflector is a tube with two mirrors inside. One mirror, a large one, is located at the end of the tube opposite the lens, the second, smaller one, is located in the middle. The rays entering the tube are reflected from a large mirror and fall on a small mirror, which is located at an angle and directs the light into a lens - an eyepiece, where we can look and see celestial objects.

Bresser Junior Reflector Telescope. Externally, a refractor is easy to distinguish from a reflector: the refractor has an eyepiece located at the end of the tube, and the reflector has an eyepiece on the side.

Which is better - a refractor or a reflector - is the subject of a real conflict between astronomy lovers. Each has its own characteristics. Refractors are simpler and more unpretentious: they are not afraid of dust, suffer less during transportation, allow for ground-based observations (since the image in them is not upside down). Reflectors are more gentle, but they allow you to observe deep space objects and engage in astrophotography. In general, refractors are more suitable for beginners, while reflectors are more suitable for advanced astronomers.

Since refractors are simpler, let’s consider the operation of a telescope using their example. Let's take the Levenhuk Strike NG series telescopes as an example - they are designed for beginner astronomers and are made with a minimum of complexity.

This is the lens that collects light. It's glass. This is why refracting telescopes are not very large: glass is heavy. The largest refractor is located at the Yerkes Observatory in the USA. The diameter of its lens is 1.02 m.

Through the lens you can see that the inside of the telescope tube is black to avoid glare from bright objects.

And this is a lens hood that protects the lens from dew. It will also protect against minor mechanical damage (shocks, blows). The lens hood also removes glare from flashlights and other nearby objects.

Eyepiece. Through it we look at the sky.

Diagonal mirror (with eyepiece and Barlow lens) - needed to ensure that the image is straight (not inverted). Then through the telescope you can observe not only space objects, but also terrestrial objects, as in the following photograph.

This photo was taken through a telescope with a digital camera. The camera is installed on the telescope using an adapter.

The camera cannot be installed on all refractors. For example, the youngest models of Levenhuk Strike NG cost 3 thousand rubles. there is no such possibility.

And finally, the most interesting thing. Pictures that can be taken with a telescope:

This photo was taken through the Levenhuk Strike 80 NG refractor in autumn, in clear weather. The moon turned out well, but it’s unlikely that planets or galaxies can be photographed well using a refractor. This is, after all, the initial model with which it is supposed to take the first steps in astronomy. But you can take it with you and use it for observing and shooting ground objects.

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Before moving on to a description of the systems and design of telescopes, let’s first talk a little about terminology, so that in the future there will be no questions when studying these astronomical instruments. So let's begin...
No matter how strange it may seem to a person unfamiliar with astronomy, the main thing in telescopes is not the magnification, but the diameter of the entrance hole ( apertures), through which light enters the device. The larger the aperture of the telescope, the more light it will collect and the fainter objects it will be able to see. Measured in mm. Designated D.
The next telescope parameter is focal length. Focal length ( F) - the distance at which the objective lenses or the main mirror of the telescope build an image of the observed objects. Also measured in mm. Eyepieces, as devices consisting of lenses, also have their own focal length ( f). Telescope magnification can be calculated by dividing the focal length of the telescope by the focal length of the eyepiece used. Thus, by changing eyepieces, you can obtain different magnifications. But their number cannot be infinite. The upper limit of magnification for each telescope is also limited. As practice shows, it is equal on average to twice the diameter of the telescope. Those. If we have a telescope with a diameter of 150 mm, then the maximum magnification that can be obtained on it is approximately three hundred times - 300x. If you set high magnifications, the picture quality will deteriorate significantly.

Another term - relative aperture. Relative aperture is the ratio of the diameter of the lens to its focal length. It is written as 1/4 or 1/9. The smaller this number, the longer the tube of our telescope (the greater the focal length).
How can we find out what size stars can be seen at the limit with our telescope?
And for this we will need a couple of simple formulas -
Limit magnitude m= 2 + 5 log D, where D is the diameter of the telescope in mm.
The maximum resolution of the telescope (i.e. when two stars have not yet merged into one point) is
r= 140 / D, where D is expressed in mm.
These formulas are valid only for ideal observing conditions on a moonless night with a wonderful atmosphere. In reality, the situation with these parameters is worse.

Now let's move on to studying telescope systems. Throughout the history of astronomy, a large number of optical telescope designs have been invented. All of them are divided into three main types -
Lens telescopes ( refractors). Their lens is a lens or a system of lenses.
Mirror telescopes ( reflectors). In these telescopes, the light entering the tube is first captured by the main mirror.
Mirror lens telescopes ( catadioptric). They use both optical elements to offset the disadvantages of both previous systems.
All systems are not ideal; each has its pros and cons.
Diagram of the main telescope systems -

Let's analyze the device of the telescope. The following illustration shows all the details of a small amateur device -

We have already heard about interchangeable eyepieces. For the convenience of observations in the near-zenith region, refracting telescopes, as well as mirror-lens instruments, often use zenith prisms or mirrors. In them, the path of the rays changes by ninety degrees and the observer becomes more comfortable when making observations (you don’t have to lift your head or climb under the telescope). Each more or less suitable telescope has seeker. This is a separate small lens device with low magnification - and, accordingly, a large field of view. (The greater the magnification of the device, the smaller the field of view). This allows you to conveniently aim at the desired area of the sky, and then examine it through the telescope itself, using high magnifications. Naturally, before making observations, you need to use the screws that clamp the finder tube to adjust it so that it is coaxial with the telescope itself. By the way, it is more convenient to do this using a bright star or planet.
Fine finishing knobs serve to adjust the pointing to an object. Fasteners movements along the axes serve to fix our telescope in the selected position. When pointing begins, the clamps (brakes) are released and the telescope is rotated in the desired direction. The position of the telescope is then fixed using these brakes, and then, looking through the eyepiece, the telescope is precisely aligned to the object using the fine adjustment knobs.
The entire set of parts on which the telescope is mounted and with the help of which it is rotated is called pry bar.
There are two types of mounts: azimuthal and equatorial. Azimuth mounts rotate around two axes, one of which is parallel to the horizon, and the other, respectively, perpendicular to the first. Those. rotation is carried out around axes - azimuth and altitude above the horizon. Azimuth mounts are more compact and convenient for use when observing terrestrial objects.
The basic astronomical mount is called equatorial. It is convenient when tracking celestial objects, as well as when pointing at them using celestial coordinates. With it, it is convenient to compensate for the rotation of the Earth, which is especially noticeable at high magnifications (do not forget that our Earth rotates and the picture of the sky continuously moves during the night). If you connect a simple motor operating at stellar speed to an equatorial mount, then the rotation of the Earth will be constantly compensated. Those. the observer will not need to constantly adjust the object using the fine motion knobs. On an equatorial mount, to compensate for the movement of the sky during the night, you only need to tighten the handle along one of the axes. In an azimuth mount, you constantly have to adjust the telescope along both axes, which is not always convenient.
Let's consider the device for an equatorial mount according to the diagram -

In an equatorial mount, one of the axes faces the celestial pole (in the northern hemisphere it is located near the North Star). The other axis, called the declination axis, is perpendicular to it. Accordingly, by rotating the telescope around each of the axes, we change its position in the celestial coordinate system. To compensate for the daily rotation of the Earth, it is enough to rotate our telescope around an axis directed to the celestial celestial pole.
How to adjust the axis direction to the celestial pole? You need to find the North Star and rotate the device with an axis that is perpendicular to counterweights(They are necessary in order to balance the weight of the telescope tube), in the direction of Polar. The height of the celestial pole of the world, as we remember, is always constant and equal to the latitude of observation. To adjust this axis in height, it is enough to set the latitude once on the latitude scale using the appropriate screws. In the future, these screws can no longer be touched (unless, of course, you move to live in other regions). It will be enough to orient the axis by turning the mount in azimuth (parallel to the horizon) so that it faces Polyarnaya. You can do this using the compass, but it is more accurate to do it using the Polar.
If we have a more or less serious mount, then for more accurate pointing at the celestial pole of the world it has a built-in pole finder. In it, on the background of the image, the corresponding marks will be visible, with the help of which you can clarify the position of the celestial pole relative to the Polar Star (remember that the Polar Star is located very close to the celestial pole, but not exactly on it!).
According to the picture that we see through the eyepiece of a telescope... Since all people have different vision, to get a good image it is necessary to focus the image. This is done using focuser- pairs of round handles on the same axis, located perpendicular to the eyepiece. By rotating the focuser knobs, you move the eyepiece assembly back and forth until an acceptable image is obtained (i.e., sharper). For mirror-lens devices, focusing is carried out using a handle moving the main mirror. You should look for it from the rear end of the pipe, also not far from the eyepiece assembly.

Well, and finally, a couple of tips for beginners using a telescope for the first time...

Necessary sequences of actions with a telescope that are worth remembering...
Finder setup.
You should pick up some bright object in the sky - a bright star or, better yet, a planet. We point the telescope at it, having previously installed the eyepiece that gives the weakest magnification (i.e., the eyepiece with the longest focal length). To quickly initially zero in on an object, you should look along the telescope tube. Having caught the image of our planet or star in the eyepiece, we lock our telescope using the axial clamps, and then center the object in the eyepiece using the fine-tuning knobs.
Next we look into the finder. By turning the screws that secure the finder tube, we ensure that the image of our object appears in the finder’s field of view and stands exactly on the crosshairs.
If we carried out the operation for too long (this happens the first time), it’s worth looking at the main device again and returning our planet (star) to the center, which, due to the rotation of the Earth (and for us, the rotation of the entire sky picture) could go to the side. Then we look at the image in the finder again and use the finder screws to correct the installation error (we set the object on the crosshair). Now our finder and telescope are coaxial.
Ideally, of course, you can then install an eyepiece with a higher magnification (with a shorter focal length) into the telescope and repeat the entire procedure described again - the accuracy of our finder tuning will increase significantly. But to a first approximation, one operation is sufficient.
After this you can observe. It is enough to adjust the alignment of the telescope and finder once at the beginning of observations.
Subsequence: We point at the telescope - look and adjust the finder.
let's move on to observations...
Targeting an object.
We release the rotation locks on both axes (brake) and, freely rotating the telescope tube, turn it in the direction we need, approximately pointing it in the direction of the object. Looking through the finder, we find the object, turning the pipe with our hands, and then fixing it with the brakes (don’t forget!), using the fine-tuning knobs we bring its image to the center of the crosshair. Now, if we have accurately adjusted the alignment of the finder and the telescope tube, the image of the object should be visible through the telescope eyepiece. We look into the eyepiece and again use the fine adjustment knobs to center the object in the field of view. All! You can admire our object and show it to others.
Subsequence: We aim at the finder and look through the telescope.
Diurnal movement of the sky.
If you have a telescope without a drive (motor) that allows you to compensate for the movement of the sky, you need to remember that after some time the object will “run away” from the field of view of the telescope. Therefore, if you are distracted for a while, then, most likely, when you look into the eyepiece, you will not find anything there. If you have an equatorial mount (with the direction previously set to the celestial pole), then it is enough to turn the fine-tuning knob along the right ascension axis by a certain angle (or maybe a rotation) so that the object returns to its “place”.
If you have an azimuth mount, then it’s a little more complicated - you’ll have to turn the knobs on both axes, and if you don’t know exactly where the object could have moved, then it’s better to look into the finder and return the object to the crosshair, looking through the eyepiece of our finder.
Image through the telescope eyepiece.
If you aim at an object and see a fuzzy image (or nothing at all), this does not mean at all that the telescope is “bad” or that the object is not in the field of view. Don't forget to focus!
In cold weather, you should wait until a telescope brought from a warm room cools down. Streams of warm air greatly spoil the image. How bigger telescope, the slower it cools. This is especially important for systems with a closed pipe - for example, mirror-lens devices.
The image and atmosphere are quite spoiled. Atmospheric turbulence, haze, and illumination from street lights make it difficult to examine objects in detail.
Finally, it should be remembered that without special filter put on the front end of the telescope tube (lens on the refractor, open part on the reflector) in no case You can't point the telescope at the Sun!!! This is fraught with loss of vision. No amount of smoked glass will help either. You should also keep an eye on the children so that they do not turn the device towards the Sun without parental supervision.
Remember - for observing the Sun, there are special filters (solar filters) that transmit a negligible part of the light from our star, for comfortable observation of it.

How to choose a telescope, what type of telescope to prefer, is a separate conversation and we will touch on it sometime in another post.

to be continued …

A telescope is an astronomical optical instrument designed for observing celestial bodies.
The telescope has an eyepiece, a lens or a main mirror and a special tube that is attached to the mount, which, in turn, contains axes through which the observation object is pointed.

In 1609, Galileo Galilei assembled the first optical telescope in human history. (Read about this on our website: Who created the first telescope?).
Modern telescopes come in several types.

Reflector (mirror) telescopes

If we give them the most simplified description, then these are devices that have a special concave mirror that collects light and focuses it. The advantages of such telescopes include ease of manufacture and good quality optics. The main disadvantage is that it requires a little more care and maintenance than other types of telescopes.
Well, now in more detail about reflector telescopes.
A reflector is a telescope with a mirror lens that forms an image by reflecting light from a mirror surface. Reflectors are used primarily for sky photography, photoelectric and spectral studies, and are used less frequently for visual observations.
Reflectors have some advantages over refractors (telescopes with a lens objective), because there is no chromatic aberration (image coloration); The main mirror is easier to make larger than a lens lens. If the mirror has not a spherical, but a parabolic shape, then the spherical shape can be reduced to zero aberration(blurring of the edges or middle of the image). Manufacturing mirrors is easier and cheaper than lens lenses, which makes it possible to increase the diameter of the lens, and therefore the resolution of the telescope. From a ready-made set of mirrors, amateur astronomers can create a homemade “Newtonian” reflector. The advantage due to which the system has become widespread among amateurs is the ease of manufacturing mirrors (the main mirror in the case of small relative holes is a sphere; a flat mirror can be small in size).

Newtonian system reflector

It was invented in 1662. His telescope was the first reflecting telescope. In reflectors, the large mirror is called the primary mirror. Photographic plates can be placed in the plane of the main mirror to photograph celestial objects.
In Newton's system, the lens is a concave parabolic mirror, from which the reflected rays are directed by a small flat mirror into the eyepiece located on the side of the tube.
Picture: Reflection of signals coming from different directions.

Gregory system reflector

Rays from the main concave parabolic mirror are directed onto a small concave elliptical mirror, which reflects them into an eyepiece placed in the central hole of the main mirror. Since the elliptical mirror is located behind the focus of the main mirror, the image is upright, whereas in the Newtonian system it is inverted. The presence of a second mirror increases the focal length and thus allows for greater magnification.

Cassegrain reflector

Here the secondary mirror is hyperbolic. It is installed in front of the focus of the main mirror and allows you to make the reflector tube shorter. The main mirror is parabolic, there is no spherical aberration, but there is a coma (the image of the point takes the form of an asymmetric scattering spot) - this limits the field of view of the reflector.

Reflector of the Lomonosov–Herschel system

Here, unlike the Newtonian reflector, the main mirror is tilted in such a way that the image is focused near the entrance hole of the telescope, where the eyepiece is placed. This system made it possible to eliminate intermediate mirrors and light losses in them.

Ritchie-Chretien reflector

This system is an improved version of the Cassegrain system. The main mirror is concave hyperbolic, and the auxiliary mirror is convex hyperbolic. The eyepiece is installed in the central hole of the hyperbolic mirror.
Recently, this system has been widely used.
There are other reflex systems: Schwarzschild, Maksutov and Schmidt (mirror-lens systems), Mersen, Nessmith.

Lack of reflectors

Their pipes are open to air currents that spoil the surface of the mirrors. Due to temperature fluctuations and mechanical loads, the shape of the mirrors changes slightly, and because of this, visibility deteriorates.
One of the largest reflectors is located at the Mount Palomar Astronomical Observatory in the United States. Its mirror has a diameter of 5 m. The world's largest astronomical reflector (6 m) is located at the Special Astrophysical Observatory in the North Caucasus.

Refractor telescope (lens telescope)

Refractors- These are telescopes that have a lens objective that forms an image of objects by refracting light rays.
This is the well-known classic long telescope in the form of a spyglass with a large lens (objective) at one end and an eyepiece at the other. Refractors are used for visual, photographic, spectral and other observations.
Refractors are usually built according to the Kepler system. The angular vision of these telescopes is small, does not exceed 2º. The lens is usually two-lens.
Lenses in small refractor lenses are usually bonded to reduce flare and light loss. The surfaces of the lenses are subjected to special treatment (coating of optics), as a result of which a thin transparent film is formed on the glass, which significantly reduces light loss due to reflection.
The world's largest refractor at the Yerkes Astronomical Observatory in the USA has a lens with a diameter of 1.02 m. A refractor with a lens diameter of 0.65 m is installed at the Pulkovo Observatory.

Mirror-lens telescopes

A mirror-lens telescope is designed to photograph large areas of the sky. It was invented in 1929 by the German optician B. Schmidt. The main parts here are a spherical mirror and a Schmidt correction plate installed at the center of curvature of the mirror. Thanks to this position of the correction plate, all beams of rays passing through it from different parts of the sky are equal in relation to the mirror, as a result of which the telescope is free from aberrations of optical systems. The spherical aberration of the mirror is corrected by a correction plate, the central part of which acts as a weak positive lens, and the outer part as a weak negative lens. The focal surface on which the image of the sky is formed has the shape of a sphere, the radius of curvature of which is equal to the focal length. The focal surface can be converted to a flat surface using a Piazzi-Smith lens.

Disadvantage Mirror-lens telescopes have a significant tube length, twice the focal length of the telescope. To eliminate this drawback, a number of modifications have been proposed, including the use of a second (additional) convex mirror, bringing the correction plate closer to the main mirror, etc.
The largest Schmidt telescopes are installed at the Tautenburg Astronomical Observatory in the GDR (D= 1.37 m, A = 1:3), the Mount Palomar Astronomical Observatory in the USA (D = 1.22 m, A = 1:2.5) and at Byurakan Astrophysical Observatory of the Academy of Sciences of the Armenian SSR (D = 1.00 m, A = 1:2, 1:3).

Radio telescopes

They are used to study space objects in the radio range. The main elements of radio telescopes are receiving antenna and radiometer- sensitive radio receiver and receiving equipment. Since the radio range is much wider than the optical range, various designs of radio telescopes are used to record radio emission, depending on the range.
When combining several single telescopes into a single network, located in different parts globe, they talk about very long baseline radio interferometry (VLBI). An example of such a network is the American VLBA (Very Long Baseline Array) system. From 1997 to 2003, the Japanese orbital radio telescope HALCA (Highly Advanced Laboratory for Communications and Astronomy), included in the VLBA telescope network, operated, which significantly improved the resolution of the entire network.
The Russian orbital radio telescope Radioastron is planned to be used as one of the elements of a giant interferometer.

Space telescopes (astronomical satellites)

They are designed for carrying out astronomical observations from space. The need for this type of observatories arose due to the fact that earth's atmosphere blocks gamma, X-ray and ultraviolet radiation from space objects, as well as most of the infrared.
Space telescopes are equipped with devices for collecting and focusing radiation, as well as data conversion and transmission systems, an orientation system, and sometimes propulsion systems.

X-ray telescopes

Designed for observing distant objects in the X-ray spectrum. To operate such telescopes, it is usually necessary to raise them above the Earth's atmosphere, which is opaque to x-rays. Therefore, telescopes are placed on high-altitude rockets or on artificial satellites Earth.

In the picture: X-ray Telescope - Position Sensitive (ART-P). It was created in the Department of High Energy Astrophysics of the Institute of Space Research of the USSR Academy of Sciences (Moscow).

It is incredibly interesting to observe the beauty of celestial bodies, especially at night, when stars, planets and different galaxies are open to view. If you want to join those who love astronomy and see all the stars, then you need to buy a telescope. Where to start? How to choose a telescope for beginners? To do this, you don’t need much - a suitable optical instrument, a star chart and a crazy interest in this mysterious science. Today you will learn what a telescope is, consider its varieties, what parameters you should pay attention to when choosing a device that will open up the world of bright stars and constellations for you.

Key questions

How to choose a telescope? Before purchasing a telescope, try to understand what you want to get from this purchase. We recommend making a list of questions and trying to answer them before heading to the store. The following questions need to be answered:

What objects do you want to see in the sky?
Where do you plan to use the device - at home or outdoors?
Do you want to pursue astrophotography in the future?
How much are you willing to spend on your hobby?
Which celestial bodies would you like to observe - the nearest planets of the solar system or the most distant galaxies and nebulae?

It is very important to give the correct answer to these questions. The device costs a lot of money, and you need to correctly decide on a specific model in order to buy a telescope that fully suits your experience and personal preferences.

Operating principle and structure of the telescope

Such an optical device is a rather complex device, thanks to which you can see even the most distant objects (terrestrial or astronomical) in a multiple magnifying glass. Its design consists of a tube, where at one end (closer to the sky) a light-collecting lens or a concave mirror is built in - a lens. On the other is the so-called eyepiece, through which we view the distant image. We'll talk about which telescope is better a little later.

The telescope design is equipped with the following additional equipment:

Search engine for detecting specified astronomical objects.
Light filters that block the strong glare of celestial bodies.
Correction plates or diagonal mirrors capable of turning the visible image that the lens transmits “upside down”.

Telescopes for professional use, which are equipped with astrophotography and video capabilities, can be equipped with the following equipment:

GPS search system.
Complex electronic equipment.
Electric motor.

Types of telescopes

Now we will introduce you to the main types of optical instruments, which differ from each other in type of design, presence of components and additional elements.

Refractors (lens)

This type of telescope is easily recognized by its rather simple design, which resembles a spyglass. The lens and eyepiece are on the same axis, and the magnifying object is transmitted along the direct spectrum - just like in the very first telescopes produced many years ago.

Such refractive optical devices can collect the reflected light of celestial objects using 2-5 magnifying convex lenses located at the two ends of a long tube structure.

How to choose a telescope for an astrology lover?

The lens apparatus is perfect for beginners to observe the life of celestial objects. Lens telescopes make it possible to clearly view both terrestrial and celestial objects beyond the boundaries of our solar system. When using a refracting telescope, you may notice that when the light caught by the lens may lose image clarity, and with repeated magnification, slightly blurred objects can be observed.

Important! It is better to use such a device in open areas, ideally outside the city, where there is no illumination of the sky by extraneous rays.

Advantages:

Easy to use and does not require additional expensive maintenance.
The sealed design of the device protects the device from dust and moisture.
Resistant to temperature changes
They can provide a clear and bright image of nearby astronomical objects.
They have a long service life.

Flaws:

Very large and heavy (the weight of some telescopes reaches 20 kg).
The maximum diameter of the magnifying lens is 150 mm.
Not suitable for urban observations.

Depending on the type of optical lenses, telescopes are divided into the following types:

Achromatic - equipped with low and medium optical magnification, but show a flat picture.
Apochromatic - produce a convex image, but eliminate defects of a fuzzy contour and the appearance of a secondary light spectrum.

Reflectors (mirror)

How to choose a telescope for observations? The work of such a telescope is to capture and transmit a light beam using two concave mirrors: the first is located inside the tube, the second refracts the image at an angle, directing it to the side lens.

Unlike a reflector apparatus, such a telescope can study deep space and obtain higher-quality images of distant galaxies. Since mirrors are cheaper than lenses, the price will be correspondingly low.

Important! It will be difficult for a novice user to manage the complex technical settings and adjustments of such a telescope. That is why we recommend that you first practice on a reflector, and later move on to a higher professional level.

Pros:

Simplicity of telescope design.
Compact size and light weight.
It captures the muted light of the most distant space objects well.
Large diameter magnifying aperture (from 250–400 mm), which conveys a more contrasting and bright image, without any defects.
Reasonable price compared to expensive refractors

Cons:

Requires special experience and time to set up the optical system.
Particles of dust and dirt may get inside the structure.
Doesn't like temperature changes.
Not suitable for viewing terrestrial and nearby solar system objects.

Catadioptrics (mirror lens)

Lenses and mirrors are the constituent elements of the lens of catadioptric telescopes. This device includes all the advantages and corrects defects as much as possible using special plates. With such a device, you can not only get the clearest picture of near and far celestial bodies, but also take high-quality photographs of the object you see.

Pros:

Small size and transportability.
They transmit the highest quality images of all existing telescopes.
Equipped with an aperture of up to 400 mm.

Cons:

Expensive.
Air accumulation inside the telescopic tube.
Complex design and control.

Telescope Selection Options

It's time to consider the main characteristics of modern optical instruments in order to understand how to choose a telescope for beginners and more.

Aperture (lens diameter)

It is the main criterion for choosing any telescope. The ability of a mirror or lens to capture light depends on the lens aperture: the higher this characteristic, the more reflected rays will hit the lens. Thanks to this, you will be able to see a high-quality image and even catch the faint visibility of the most distant space objects.

When choosing an aperture based on your goals, focus on the following numbers:

To see clear details in the image of nearby planets or satellites, a telescope with a diameter of up to 150 mm is sufficient. For urban conditions, this figure can be reduced to 70–90 mm.
A device with an aperture of more than 200 mm will be able to view more distant celestial objects.
If you want to see near and far celestial bodies outside the city, you can try the largest optical lens size – up to 400 mm.

Focal length

The distance from celestial bodies to a point in the eyepiece is called the focal length. It is here that all light rays form a beam of a single glow. This indicator dictates the degree of magnification and clarity of the visible image - the higher it is, the better we will see the celestial body of interest. The higher the focus, the longer the telescope itself, so such dimensions can affect the compactness of its storage and transportation.

Important! A short-focus device can be kept at home, but a long-focus device can be kept in a larger room, for example, in the courtyard of a house or in a country house.

Magnification ratio

This indicator can be easily determined by dividing the focal length by the characteristics of your eyepiece. So, if the diameter of the telescope is 800 mm, and the eyepiece is 16, then you can get 50x optical magnification.

Important! If you install a weaker or more powerful eyepiece, you can independently adjust the magnification of various objects.

Today, manufacturers offer various optics - from the lowest (4–40mm) to the highest, which can double the focus of an optical device.

Mount type

This is nothing more than a telescope stand. Its direct purpose is to make the telescope easy to use.

The amateur and semi-professional set consists of 3 main types of such movable supports:

Azimuthal is a fairly simple stand that moves the device horizontally and vertically. Refractors and catadioptrics are equipped with this type of support. An alt-azimuth mount is not suitable for astrophotography, as it is not able to capture a clear image of the object.
Equatorial - has an impressive weight and dimensions, but it perfectly finds the desired star at given coordinates. This type of mount is suitable for reflectors that capture the most distant galaxies. The equatorial support is very popular among astrophotography enthusiasts.
The Domson system is a cross between a regular cheap azimuth stand and a sturdy equatorial design. Very often it is added to a package with powerful reflectors.

You should not overpay for the dimensions of the telescope. It should be such that you can carry and transport it yourself. The best telescope for home should be as compact and easy to use as possible.
If you transport the device in a car, you need to make sure that the dimensions of the pipe allow it to be placed in the cabin or trunk. Otherwise, you will have to repair not only the telescope, but also your truck.
Choose a location in advance to view celestial objects. The best option there will be a place that is outside the city. If you do not have transport, then stop at the nearest observation point with the absence of nearby residential areas and other buildings.
If you are a beginner, then do not spend your entire accumulated budget at once. Purchasing eyepieces, powerful filters and other equipment is a very expensive process.
Try to observe the celestial bodies as often as possible. So, if you use a telescope every day and look at the same objects, then over time you can see their new changes and movements.
If your goal is to study the most distant galaxies and nebulae, then buy a reflector with a diameter of 250 mm or more, complemented by an azimuthal stand.
Fans of astrophotography cannot do without a catadioptric optical device with a powerful aperture (400 mm) and the longest focusing distance from 1000 mm. An automatic equatorial mount can be added to the kit.
You can give your child a budget and easy-to-use refractor telescope from the children's series, equipped with a 70 mm aperture on an azimuthal support. And an additional adapter will help you take spectacular photos of the Moon and ground objects.

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We really hope that after reading our article, you have become an expert in the field of telescopy, and choosing a good telescope for your home will not be a problem for you. Observing the Moon, stars, planets, galaxies, and interesting nebulae is extremely exciting and extremely interesting! We wish you new discoveries and long service life of your telescope!

To magnify an observed astronomical object, you need to collect light from this object and focus it (i.e., the image of the object) at some point.
This can be done either by a lens made of lenses or by a special mirror.

Types of telescopes

*Refractors - light is collected by a lens lens. It also creates an image of an object at a point, which is then viewed through the eyepiece.
*Reflectors - light is collected by a concave mirror, then the light is reflected by a small flat mirror to the surface of the telescope tube, where the image can be observed.
*Mirror-lens (catadioptric) - both lenses and mirrors are used together.

Choosing a telescope

Firstly, the magnification of a telescope is not its main characteristic! The main characteristic of all telescopes is the aperture= lens (or mirror) diameter. A large aperture allows the telescope to collect more light, therefore, the observed body will be clearer, details will be better visible, and higher magnifications can be used.

Next, you need to find out which stores in your city sell telescopes. It is better to buy in stores that specialize in selling only telescopes and other optical instruments. Otherwise, carefully check the telescope: the lenses must be free of scratches, all eyepieces, assembly instructions, etc. must be included in the kit. You can also order a telescope through an online store (for example, here). In this case, you will have more choice. Don't forget to find out the telescope delivery and payment methods.

Pros and cons of the main types of telescopes:

Refractors: more durable, they require less maintenance (as the lenses are in a closed tube). The image obtained through a refractor is more contrasting and saturated. 100% transmits light (with a coated lens). Temperature changes have little effect on image quality.
-Refractors: more expensive than reflectors, the presence of chromatic aberration. (in apochromatic refractors it is less pronounced than in achromatic refractors) Low aperture ratio.

Reflectors: cheaper than refractors, no chromatic aberration, short tube length.
-Reflectors: the need for adjustment (installation of all optical surfaces in their calculated places), lower image contrast, open pipe (=>mirror contamination). The silver coating on the main mirror may deteriorate after a few years. When you take the telescope out of a warm room into cold air, the mirror fogs up - up to 30 minutes of downtime are required. Reflectors transmit 30-40% less light than refractors with the same aperture.

Mirror-lens: compact, lack of chromatism and some other distortions that are found in reflectors. The pipe is closed.
-Mirror-lens: high light loss due to reflections in mirrors, quite heavy, high price.

The first criterion when choosing a telescope is the aperture. The rule always applies: the larger the aperture, the better. True, a telescope with a larger aperture is more influenced by the atmosphere. It happens that a star can be seen better in a telescope with a much smaller aperture than with a larger one. However, outside the city or when the atmosphere is stable, a telescope with a larger aperture will reveal much more.

Don’t forget about the optics: it must be glass and coated.

It's important to know that a 100mm refractor is roughly equivalent to a 120-130mm reflector (again due to the reflector not having 100% light transmission).

->About telescope magnification: the maximum useful magnification of the telescope, at which the image will be more or less clear, is approximately 2*D, where D is the aperture in mm (for example, for a 60 mm refractor, the maximum useful magnification is: 2*60=120x). But! everything again depends on the optics: with a 60 mm refractor, with normal optics and atmosphere, you can get a clear image up to 200x, but no more!).

->You can find telescopes with different focal lengths of the lens. A long-focus telescope usually gives a better image than a short-focus telescope (because a short-focus telescope is more difficult to make without distortion). However, a long lens focus means a long telescope tube - an increase in dimensions

->Another characteristic of a telescope is the relative aperture - the ratio of the lens diameter to the focal length. The larger the relative aperture (1/5 is larger than 1/12), the brighter the image of the luminaries will be; on the other hand, the distortions will be more noticeable.

A refractor with an aperture ratio of 1:10 ~ corresponds to a reflector with an aperture ratio of 1:8

->Choose a telescope based on its dimensions: if you often move the telescope (traveling out of town, for example), a small telescope will be more convenient, not too long and not too heavy. If the telescope will not be taken out, you can take a larger one.

->It is worth paying attention to the tripod and mount of the telescope. With a weak tripod, the image will wobble every time you touch the telescope (the higher the magnification selected, the more wobble it will be)

There are two types of mounts: azimuth and equatorial:

An azimuth mount allows you to point the telescope at an object along two axes - horizontal and vertical.
Equatorial - one of the axes of rotation of the telescope is parallel to the axis of rotation of the Earth.

Pros and cons different types pry bars

Azimuthal: a very simple device. Cheaper than equatorial. Weighs less than the equatorial one.
-Azimuthal: the image of the star “runs away” from the field of view (due to the rotation of the Earth around its axis) - it is necessary to redirect the telescope along two axes (the higher the magnification, the more often) => it will be more difficult to photograph the star.

Equatorial: when the star “runs away” - by moving one handle of the mount, you will “catch up” with it.
-Equatorial: heavy weight of the mount. At first it will be difficult to master and set up the mount (more about setting up)

There are electric equatorial mounts - you won't need to re-aim the telescope - the equipment will do it for you

If you buy in a store, do not be lazy: carefully inspect the telescope: there should be no scratches, chips or other defects on the lenses and mirrors. The kit must include all the eyepieces declared by the manufacturer (you can see in the instructions what should be included in the kit).