The telescope is designed for... Review of modern telescopes and their key characteristics. What does a telescope give a person?

In the 17th century, an instrument called a telescope was invented. What is it for? Thanks to him, it became possible to observe the movement of planets, the formation of galaxies and the study of the mysterious. The view through the telescope is incredible and... it is available to anyone person interested in astronomy.

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Operating principle of the device

What is a telescope ? This is a tool with which you can observe a distant object, thanks to certain lenses and electromagnetic radiation from the object itself. How many times does this technique increase?

It all depends on the model: the simplest children's telescopes are 10 times, and the most powerful Hubble is more than 1000 times.

The telescope works by refraction of light and a set of correctly selected lenses. It's all about the ability of the optics to collect light, and the larger its lens, the more light it collects and, accordingly, the better it transmits the image.

From this it follows that it is light, or rather its quantity, plays a role in the quality of the final image and its details. The diaphragm is responsible for collecting light - a plate with a hole through which light rays pass, so when purchasing optics you should pay great attention to this particular detail.

Important parameters

In addition to the diaphragm, there are others, no less important details. These include:

1. Lens diameter – it is responsible for the instrument’s ability to collect light: the larger this parameter, the smaller the details can be seen.
2. Focal length is the distance from the lens to the focus, and it is responsible for the magnification power of the device.
3. An eyepiece is two or more lenses held together by a cylinder whose job is to magnify the resulting image.
4. Lens – forms the image. A Barlow lens is often used and can double the focal distance.
5. Diagonal mirror - with its help you can deflect the flow of light at an angle of 90°. This is convenient when you need to observe bodies located strictly vertically above the observation site.
6. Viewfinders are an additional tool that is used in conjunction with the main equipment.
7. Straightening prisms - since images come out upside down, these details help to correct and view them at an angle of 45°.
8. Mounts are devices that can be used to secure and point equipment.

When purchasing a device, you should carefully read these details to choose the best option for your purpose.

Kinds

Like any optics, there are telescopes:

1. Amateur optics are optics that can magnify objects several hundred times;
2. Professional scientific ones are higher quality and more powerful instruments.

Types of telescopes

Professional and scientific are divided on the:

• optical – magnify more than 250 times, but after this threshold the quality of the pictures begins to deteriorate;
• radio telescopes - they measure the energy of objects and provide the highest quality image;
• X-ray;
• Gamma-ray telescopes.

In addition, they are divided and by optical class:

• refractive – they use a large lens as a light-gathering part;
• reflective - with a concave mirror that collects the light flux and forms a picture;
• mirror-lens - in this optics both types of light-collecting parts are used simultaneously.

Some instruments in space are needed to take better pictures. They grouped by radiation frequencies:

• gamma;
• X-ray;
• ultraviolet;
• visible;
• infrared;
• microwave;
• radio emission.

note! A certain optical device captures the radiation and, based on it, builds a picture that is transmitted to the observatory. On Earth, the most popular devices are reflex technology, which is used by both amateurs and professionals.

What is visible

Optical instruments are necessary for space exploration. The most convenient telescope for this is After all, it can be seen quite clearly:

1. The moon - with special optics you can see its detailed relief, and even its ashen light;

Telescope and starry sky

Available for study:

• Mercury - it will be visible like a star, and only with lenses larger than 100 mm in diameter can you observe the phase of the planet in the form of a small crescent;
• Venus is the brightest celestial body, it is easy to see the phase of the planet using any technique;
• - will be visible as a small circle and only 2 times a year;
• Jupiter - even with a homemade telescope, Galileo was able to examine its 4 satellites, so it is easy to fully examine this planet and its rings;
• Saturn is the most beautiful planet in the system. It will be visible along with the rings even through 50-60 mm lenses;
• Uranus and Neptune - these distant planets, even with professional lenses, look like small stars or blue disks.

Important! You should never try to look at it with a telescope. This will cause permanent eye damage and equipment damage.

What else is possible see through a telescope:

1. Star clusters - they can be viewed through optics with any diameter, but only through lenses with a diameter of 100-130 mm will individual stars be visible.
2. Galaxies - distant systems of planets and stars are visible even with simple binoculars, but with lenses of 90-100 mm, you can already observe their shape, and with lenses with a diameter of 200-250 mm you can even see the stellar arms.
3. Nebulae are clouds of gas and dust that are illuminated by stars. With amateur equipment, you can see them as faint spots, but more professional equipment will show their gas structure.
4. Double stars - stars can not only be lonely like the Sun, but also represent a system of two, three or more copies. With special instruments, even double stars can be seen as points, since they are located at a great distance from the Earth.
5. Comets—“tailed guests”—can be seen with your eyes, but through eyepieces you can even see their tails in detail.

Stargazing is a fascinating activity that not only develops, but also gives an idea of ​​the entire Universe. And so that what you see can be understood, you should use it in these classes. special star map.

How to choose a device for observing planets

Due to the abundance of optical instruments on the market, it is quite difficult to decide which technology to choose for observing planets. To simplify this process, you should pay attention to the diameter of the pipe - it is the aperture (diameter) that determines everything optical capabilities of the device.

The larger it is, the more light the lens transmits and, accordingly, the larger and better the final image and the ability to enlarge objects.

To calculate the maximum magnification, you should use the formula: 2x D, where D is diametrical millimeters. You should also consider the ultimate goal: will the technology be used to observe nature or space? What is the level of an astronomer? Based on the answers, you should choose. You should pay attention on the:

• aperture;
• focal length;
• lenses or mirrors;
• presence of a reflector.

The most important parameter of all is the aperture. What is this? This is the diameter of the lens. Why do you need the correct size? Based on it, you can simply look at distant spots, or in detail study the celestial body. These models should be chosen for novice astronomers:

• Sky-Watcher;
• Arsenal-GSO;
• Celestron.

What is best for a child?

Are there any differences between adult and children's technology for observing the sky? Of course, and the main one is increase. Children's specimens never will not enlarge the image just like the cheapest and simplest adult. But the advantages of children's options are in their size - they are all quite compact and easy to transport. Through such lenses you can see:

• Earth's satellite and its relief;
• constellations;
• all the planets in the solar system;
• Milky Way;
• Clusters of stars;
• nebulae.

Does a child need a telescope?

Of course, if he shows interest in science and astronomy.

Despite the small image, the child will be able to see almost all celestial bodies, which will not only satisfy his interest, but also encourage him to learn and explore the world.

Therefore, you should approach the choice carefully and pay attention to some characteristics of the purchased equipment:

• system: lens or mirror;
• focal length (ideal for a child is from 520 to 900 mm);
• lens diameter (from 40 to 130 mm).

Which models are ideal for a baby? Can choose:

• Bresser Junior;
• Levenhuk;
• Bresser Space;
• Sky-Watcher Dob.

Which telescope should I choose for my child? It is best to take a refractor in models specifically for children. It is easy to use and does not require settings.

Advice! There are devices with an auto-guidance system that can search for objects in the sky independently according to specified parameters.

For photography

How to photograph through such optics? For this you need a telescope and any camera. Photos can be taken even with the simplest model and mobile phone. For example, ocular projection is obtained by shooting even with a phone through the eyepiece. For better photographs, you will need a camera with a lens that can be removed, and a tripod, which should be used to avoid shaking hands. Photographs are also taken through an adjusted eyepiece, and it is best to shoot in clear weather to obtain a clear and high-quality image.

Why are telescopes needed, their functions

What can you see with a telescope

Conclusion

The ability to see does not come immediately. Experienced astronomers spend many hours using telescopes before they can independently discern small objects or distant stars. This talent develops just like any other, so you need to be patient and practice regularly.

How to choose a good optical instrument?

As soon as a person establishes visual contact with space, he seeks an opportunity to look at everything that he sees much closer, to examine as many details as possible. This is what a telescope is designed for, how to choose it correctly?

Nowadays, so many different designs and models have been created that the buyer is at a loss for a long time - not knowing where to start buying. To begin with, of course, you should decide what you want to see in it and under what conditions you will observe it all. It is imperative to evaluate the living conditions in order to allocate a place for it, and material capabilities, that is, the funds that you can afford to pay for it. However, for the same amount you can buy two different tools.

Types of telescopes

In order to see the galaxy and nebulae, the largest aperture is needed. The usual dimensions of refractor rulers, for some reason, end at around 150 mm. Newtonian telescopes are most suitable for these purposes.

Photographs of planets are most often used using catadioptric telescopes, but they will be unsuitable for photographing a weakly extended object due to the small aperture.

Refractors are very suitable for observing star fields and double stars. You can also use them to view the moon and planets.

Conclusion

The mistake many buyers make is wanting to buy one telescope once and for all. You need to understand that each tool is intended for different objects, performs its role and will reveal to you different secrets of our universe. Of course, the enjoyment of your excursion through space will largely depend on you, and not on the telescope. Using even inexpensive tools, you can make your research interesting and unforgettable.

Video guide that describes in detail how to choose a telescope

OPTICAL TELESCOPE

OPTICAL TELESCOPE - used to obtain images and spectra of space. objects in optical range. electron-optical converters, charge-coupled devices. The efficiency of an optical telescope is the magnitude achievable on a given telescope for a given signal-to-noise ratio (accuracy). For weak point objects, when determined by the background of the night sky, it depends mainly. from attitude D/,Where D- aperture size O. t., - ang. diameter of the image it produces (the larger D/,the greater, all other things being equal, is the limiting magnitude). Operating at optimum. O. t. conditions with a mirror diam. 3.6 m has a maximum stellar magnitude of approx. 26 T with an accuracy of 30%. There are no fundamental restrictions on the maximum stellar magnitude of terrestrial stars.
Astr. O. t. was invented by G. Galilei in the beginning. 17th century (although he may have had predecessors). HisO. i.e. had a scattering (negative) . Approx. in the same I. sighting accuracy. Throughout the 17th century. Astronomers used optical telescopes of a similar type with a lens consisting of a single flat-convex lens. With the help of these orbitals, the surface of the Sun (spots, torches) was studied, the Moon was mapped, the satellites of Jupiter and the reflector were discovered. With the help of similar orbitals, W. Herschel discovered Uranus. Progress of glass making and optical theory. systems made it possible to create in the beginning. 19th century achromatic Achromat). The optical telescopes using them (refractors) were relatively short in length and gave a good image. Using such optical telescopes, distances to the nearest stars were measured. Similar tools are still used today. The creation of a very large (with a lens diameter of more than 1 m) lens refractor turned out to be impossible due to the deformation of the lens under the influence of its own. weight. Therefore, in con. 19th century The first improved reflectors appeared, which consisted of a concave parabolic made of glass. shape, coated with a reflective layer of silver. With the help of similar O. t. in the beginning. 20th century Distances to nearby galaxies were measured and cosmological discoveries were made. redshift.
The basis of optical technology is its optics. system. A). Optical option system is the Cassegrain system: a beam of converging rays from Ch. parabolic the mirror is intercepted to focus by a convex hyperbolic. mirror (Fig. b). Sometimes this focus is carried out into a stationary room (where) with the help of mirrors. Working field of view, within the optical range. modern system large O. t. builds undistorted images, does not exceed 1 - 1.5°. The wider-angle O. surface is placed at the center of curvature of the spherical surface. mirrors Maksutov systems have aberrations (see. Aberrations of optical systems)ch. spherical mirrors are corrected by a meniscus with a spherical field of view up to 6°. The material from which O. t. mirrors are made has low thermal properties. coefficient expansion (TCR) so that the shape of the mirror does not change when the temperature changes during observations.

Reflecting telescopes take advantage of the fact that shaped mirrors produce results very similar to lenses. Reflecting telescopes suffer from another kind of distortion called spherical aberration, where light rays from different locations are focused at different points. This is because the surface is spherical, hence the name. Although it can be difficult, this aberration can be eliminated by adjusting the mirror to a perfect parabolic shape.

Catadioptric telescopes use a mixture of lenses and mirrors to maximize light collection and minimize telescope distortion. An optical telescope collects light and focuses it to form an image. Astronomers use telescopes that cover the entire electromagnetic spectrum, but the first telescopes were purely optical telescopes. Galileo was the first known scientist to use a telescope for astronomy; Before his time, our ability to produce high-quality lenses was insufficient to create such a telescope.

Some optical designs of large modern reflectors: A- direct focus; b- Cassegrain trick. A- main mirror, IN - focal surface, arrows indicate the path of rays.

Optical elements of the O.T. are fixed in the O. pipe. t. To eliminate decentration of optics and prevent deterioration in image quality when the pipe is deformed under the influence of the weight of parts of optical t. n. compensation pipes type that do not change the direction of the optical fiber when deformed. Installation (mounting) of the O.T. allows you to point it at a selected cosmic location. object and accurately and smoothly accompany this object in its daily movement across the sky. The equatorial mount is widespread: one of the axes of rotation of the O. t. (polar) is directed towards the world (see. Astronomical coordinates) and the second is perpendicular to it. In this case, the object is tracked in one motion - rotation around the polar axis. With an azimuth mount, one of the axes is vertical (computer) - by turning in azimuth and height and rotating the photographic plate (receiver) around the optical. axes An azimuthal mount makes it possible to reduce the mass of the moving parts of the pipe, since in this case the pipe rotates relative to the gravity vector in only one direction. O. t. installed in special. towers. The tower must be in thermal equilibrium with the environment and with the telescope. Modern O. t. can be divided into four generations. The 1st generation includes reflectors with a main glass (TKR 7x 10 -6) parabolic mirror. shapes with a thickness to diameter ratio (relative thickness) of 1/8. The tricks are direct, Cassegrain and coude. The pipe - solid or lattice - is made according to the principle of max. rigidity. O. t. of the 2nd generation is also characterized by parabolic. Ch. mirror. Tricks - direct with corrector, Cassegrain and coude. The mirror is made of pyrex (glass with TKR reduced to 3 x10 -6), relates. thickness 1/8. Very rarely, the mirror was made lightweight, that is, it had voids on the back side. reflector of the Mount Palomar Observatory (USA, 1947) and a 2.6-meter reflector of the Crimean Astrophysics. Observatory (USSR, 1961).
O. t. 3rd generation began to be created at the end. 60s They are characterized by optical scheme with hyperbolic Ch. mirror (the so-called Ritchie-Chretien scheme). Focuses - direct with corrector, Cassegrain, quartz or glass-ceramic (TKR 5 x 10 -7 or 1x 10 -7), relative. thickness 1 / 8 . Pipe compensation scheme. Hydrostatic bearings. Example: 3.6-meter reflector of the European Southern Observatory (Chile, 1975).
O.t. 4th generation - instruments with mirror dia. 7 - 10 m; They are expected to enter service in the 90s. They involve the use of a group of innovations aimed at meaning. reducing the weight of the tool. Mirrors - made of quartz, glass-ceramic and, possibly, pyrex (lightweight). Refers. thickness less than 1/10. Compensation pipe. The world's largest telescope is a 6-meter telescope installed in the Special. astrophysics observatory (SAO) of the USSR Academy of Sciences in the North Caucasus. The telescope has a direct focus, two Nasmyth focuses and a focuskude. The mount is azimuth.
O. t., consisting of several, have a well-known perspective. mirrors, the light from which is collected in a common focus. One of these O. t. operates in the USA. It consists of six 1.8-meter parabolics. Solar telescopes are characterized by very large spectral equipment, which is why the mirrors are usually made motionless, and the light of the Sun is applied to them by a system of mirrors called a coelostat. Diameter modern solar O. t. is usually 50 - 100 cm. Astrometric. O. t. (intended to determine the positions of space objects) are usually small in size and higher. mechanical stability. O.t. for photography astrometry have special. To eliminate the influence of the atmosphere, it is planned to install O. t. in space. devices.

There are three types of telescopes: refractive, reflective and catadioptric. Refracting telescopes use lenses to focus light, reflecting telescopes use curved mirrors, and catadioptic telescopes use a mixture of both. Refracting telescopes may suffer from chromatic aberration, and reflecting telescopes may suffer from spherical aberration. In both cases, the image becomes blurry. Chromatic aberration can be corrected using multiple lenses, while spherical aberration can be corrected using a parabolic mirror.

Lit.: Methods of astronomy, trans. English, M., 1967; Shcheglov P.V., Problems of optical astronomy, M., 1980; Optical telescopes of the future, trans. from English, M., 1981; Optical and infrared telescopes of the 90s, trans. from English, M., 1983.

P. V. Shcheglov.

Physical encyclopedia. In 5 volumes. - M.: Soviet Encyclopedia. Editor-in-chief A. M. Prokhorov. 1988 .

What a person sees with the eyes depends on the resolution that can be achieved on the human retina. However, this is not always satisfactory. For this reason, since ancient times, milled rock crystals have been used as so-called "Lesstein" to compensate for transparency due to old age and to serve as a magnifying glass.

The development of such materials in high quality and in any quantity of detail was largely a material development of glass for the production of "lenses" - as these optical components were soon named because of the typical geometry - a story unto itself. The same applies to its processing and finishing by grinding and polishing.

- (Greek, this. See telescope). An optical instrument, a telescope, with the help of which objects located at a far distance are examined; used more for astronomical observations. Dictionary of foreign words included in... ...

- (from the word optics). Related to light, to optics. Dictionary of foreign words included in the Russian language. Chudinov A.N., 1910. OPTICAL from the word optics. Relating to light. Explanation of 25,000 foreign words that came into use in... ... Dictionary of foreign words of the Russian language

Therefore, the path to an optical telescope is directly related to the development of reading tools. Especially from the beginning to the end of the century, glasses can make good progress, as evidenced by archaeological finds. Nearsightedness was primarily disadvantaged because the concave lenses needed to correct this type of defective vision were difficult to manufacture to satisfactory quality, unlike convex ones.

The question remains as to who first held a strong concave lens close to the eye and a weak convex lens at some distance one after the other and thus discovered the basic principle of the telescope. This year he proposed the first such tubular liner combination to Dutch authorities as a weapon-defining tool. At this time, the Netherlands was fighting for independence, and its fighters were interested in being able to observe the enemy from a great distance without being exposed to risk.

telescope- a, m. telescope m., n. lat. telescopium gr. far seeing. 1. An optical device for observing celestial bodies. BAS 1. Late in the evening he was walking... he had a hand telescope in his hand, he stopped and took aim at some planet: it was puzzling... Historical Dictionary of Gallicisms of the Russian Language

However, the patent was suspended because two other Dutch glasses, Zacharias Janssen and Jakob Adriaanzoon Metius, appeared at the same time. Although at first only distant objects were discovered on earth, it took a short time for naturalists to also turn to the skies.

His improvement proposals, and those of his contemporaries and successors, aimed to improve the telescope's usability, resolution, and image quality. Their constant implementation resulted in the fact that celestial bodies were always more closely observed and that the interactions between individual astronomical objects could be studied more and more precisely. This ultimately revolutionized man's self-awareness in space and led to interpretations that are now commonplace: be it the acceptance of a heliocentric worldview, the number of planets and satellites in our solar system, or the fact that our sun is just one of an unimaginably many stars are again located in one of the billions of galaxies.

TELESCOPE (Telescopium), a faintly visible constellation in the Southern Hemisphere. The brightest star is Alpha, 3.5 magnitude. TELESCOPE, a device for obtaining magnified images of distant objects or studying electromagnetic radiation from ... ... Scientific and technical encyclopedic dictionary

A device in which standing or running electricity can be excited. mag. optical waves range. O. r. is a collection of several mirrors and phenomena open resonator, unlike most cavity resonators used in the range... ... Physical encyclopedia

The road to this realization was wide and posed many technical challenges. Since the invention of the telescope, all its components have been experimented with, their limits recognized and improved. The following sections briefly describe selected developments in this area.

The key elements here are the components that direct and collect the light, the measuring instruments and receivers that capture and record that light, and the mechanical components that house or advantageously organize the optics and detectors.

TELESCOPE- An optical instrument that helps the eye or camera to observe or photograph distant objects, magnify celestial bodies and focus the flow of light, increasing the clarity of the image. From some ancient reports it can be concluded that the telescope... ... Astrological encyclopedia

Optical telescopes are divided into two categories: lens telescopes and reflecting telescopes. Both telescopes were invented at the beginning of the century, but the telescope was about ten years earlier than the reflecting telescope. Today, refractors are essentially used only by hobby astronomers, while all scientifically used telescopes, and large telescopes in particular, are reflectors.

Lens Reflectors A refractor consists of two lenses: an objective lens, a collection lens, and an eyepiece, depending on the design, a collection lens, or a diverging lens. The Kepler telescope of two collectible lenses is a common design of modern refractors, the image rotated 180 degrees is often properly aligned by additional optical elements. Objective telescopes have two very important disadvantages: on the one hand, the dependence of the refractive index on the wavelength leads to an aberration error, chromatic aberration: light beams of different wavelengths converge at different coordination points.

Telescope (from tele... and Greek: skopéo I look), an astronomical optical instrument designed for observing celestial bodies. According to their optical design, telescopes are divided into mirror (reflectors), lens (refractors) and mirror-lens... ... Great Soviet Encyclopedia

TELESCOPE, telescope, man. (from the Greek tele into the distance and skopeo I look). 1. Optical instrument for observing celestial bodies (astron.). 2. A fish of a reddish-golden color with extremely bulging eyes (zool.). Ushakov's explanatory dictionary. D.N. Ushakov... ... Ushakov's Explanatory Dictionary

This effect can be reduced by increasing the focal length of the lenses. This resulted in the last large refractors being extremely large and therefore difficult to handle at the end of the century. On the other hand, lenses of any size cannot be used.

Large lenses are very heavy and difficult to mount and stabilize due to their weight and because they can only be attached to the edge. The technical limit is about one meter. Mirror Telescopes After the technical limits of telescopes lenses were reached towards the end of the century, mirror telescopes finally released them because they are not subject to the same aperture limitation, and in the case of mirrors, chromatic aberration does not occur. A reflecting telescope essentially consists of two mirrors: the main or main mirror and the catch or some of these designs are shown in the following.

If you are a “typical” astronomy enthusiast who owns a telescope, then you have probably asked yourself more than once: how high-quality images does it show? There are many products on sale whose quality is easy to evaluate. If, say, you are offered to buy a car that cannot accelerate faster than 20 km/h, you will immediately realize that there is something “wrong” with it. But what about a newly purchased or assembled telescope, how do you know if its optics are “working” at full power? Will it ever be able to demonstrate the kinds of celestial objects you expect from it?

The telescope on the roof of the Göttingen Institute for Astrophysics is a Cassegrain telescope. Since light does not penetrate the mirror, the entire underside can be used for mounting. Therefore, in principle, the size of the mirror is not subject to any size limitation. The largest two-piece mirror with a diameter of 8.4 meters is the Large Binocular Telescope. Larger mirror diameters are achieved through segmentation. The Hobby-Eberly Telescope mirror, for example, consists of 91 hexagonal elements with a diameter of one meter and is actually equivalent to a 9.2-meter mirror.

Fortunately, there is a simple but very accurate way to test the quality of optics that does not require any special equipment. Just as you don't need to know the theory of an internal combustion engine to determine that an engine is running poorly, you don't need to be familiar with the theory of optical design to judge the quality of a telescope. By mastering the testing techniques discussed in this article, you can become an authoritative judge of optical quality.

The European Extremely Large Telescope is estimated to have an effective diameter of 42 meters. As in radio astronomy, interference is also a common method of optical observation. The four 8.2-meter telescopes of the Very Large Telescope can be interferometrically interconnected. The Hubble Space Telescope, undisturbed by the Earth's atmosphere, partially observes in the optical frequency range.

Installation In addition to the telescope itself, its installation is also necessary. The telescope must be very durable, but at the same time mobile. Maximum coverage of the visible sky requires two axes. In an equatorial mount or parallax mount, one of the two axes is aligned parallel to the Earth's axis of rotation. The rotation angle of the other axis then exactly corresponds to the declination of the observed object. This mount allows you to simply track the telescope to compensate for the Earth's rotation, which only requires rotation around its axis.

PERFECT IMAGE

Before you start talking about quality, you need to know what an ideal image of a star should look like through a telescope. Some novice astronomers believe that in an ideal telescope, a star should always appear as a bright and sharp point of light. However, it is not. When observed at high magnifications, the star appears as a small disk surrounded by a series of faint concentric rings. This is called a diffraction pattern. The central disk of the diffraction pattern has its own name and is called the Airy circle.

In this case, the facial field remains unchanged, so that long-term exposure to expanded objects can be made. On the other hand, the azimuth mount is more stable and is therefore used in particular in large telescopes. It has a vertical axis and a horizontal axis. Tracking is much more difficult because both axes must move at constantly changing speeds. This is, however, easily possible with computer controlled stepper motors. Rotation of the face field during tracking is inevitable.

Flat objects are thus washed out during long exposures. To avoid this, several short exposures must be made instead, and the individual images must be rotated before overlaying them. It is also necessary to take into account the installation of additional devices - also when choosing a telescopic type. Thus, the second axis is almost replaced by the rotation of the earth. However, the observable part of the sky is more limited.

This is what the diffraction pattern should look like in an ideal telescope. Please note that the diffraction rings look exactly the same on opposite sides of the focus. In telescopes that have a secondary mirror (screening), a dark area appears in the center of the defocused image. All illustrations shown in the article were simulated using a computer. In all illustrations, the image in the center is exactly in focus, the two on the left are in front of focus (closer to the lens), and the two on the right are behind focus (further from the lens).

A siderostat or heliostat allows light to be fed into a static telescope. The siderostat on the roof of the Göttingen Institute for Astrophysics consists of two rotating and rotating plan mirrors that direct the light of the sun and bright stars into a vertical telescope built into the building. The start of construction of the world's largest optical telescope has fallen: in the Atacama Desert in Chile, representatives of the European Southern Observatory and the Chilean government took part in a ceremony to begin construction.

With the help of a giant telescope it would also be possible to detect life in the Universe. The telescope will also yield new findings on dark matter. The festive hour was marred by a small problem. However, the construction of the telescope will not be delayed. The extremely large telescope has a mirror with a diameter of 39 meters. Currently, the largest telescopes have a maximum of ten-meter mirrors. A budget of one billion euros is estimated for the first phase of construction.

What causes these rings to appear and the star to turn into a disk? The answer to this question lies in the wave nature of light. When light passes through a telescope, it always experiences “distortions” caused by its design and optical system. Not a single most remarkable telescope in the world is able to reproduce the image of a star in the form of a point, since this contradicts the fundamental laws of physics. Laws that cannot be broken.

The accuracy of image reproduction produced by a telescope depends on its aperture - the diameter of the lens. The larger it is, the smaller the angular dimensions of the diffraction pattern and its central disk become. This is why telescopes with larger diameters can separate closer binary stars and allow us to see more detail on planets.

Let's conduct one experiment with which you can find out what the diffraction pattern of an almost ideal lens looks like. This image will become the standard with which you will subsequently compare the actual diffraction patterns of the instruments being tested. For the experiment to be successful, we will need a telescope with intact and fairly well-adjusted optics.

First of all, take a sheet of cardboard or thick paper and cut a round hole with a diameter of 2.5-5 cm in it. For telescopes with a focal length of the lens less than 750 mm, a hole of 2.5-3 cm is suitable; for a larger focal length of the lens, cut a hole with a diameter of 5 cm.

The resulting sheet of cardboard must be secured in front of the lens so that the hole, if you have a refractor, is in the center, and if you have a reflector, it is slightly on the edge, so that the incoming light passes the secondary mirror and the stretch marks of its attachment to the pipe.

Point the telescope at a bright star (such as Vega or Capella) that is currently high above the horizon, and set the magnification to 20 to 40 times the lens diameter in centimeters. Looking through the eyepiece, you will see a diffraction pattern - a spot of light surrounded, depending on the calmness of the atmosphere, by one or more concentric rings.

Now begin to slowly defocus the image of the star. At the same time, you will see expanding rings originating in the center of the light spot, just as waves diverge from a stone thrown into water. Defocus the image until you see 4-6 of these rings. Notice that the light is distributed more or less evenly across the rings.

Having memorized the type of diffraction pattern, begin to move the eyepiece in the opposite direction.

Once you pass the focal point, you will again see expanding rings of light. Moreover, the picture should be completely similar to the previous one. The image of the star on both sides of the focus should look exactly the same - this is the main indicator of the quality of the optics. High-quality telescopes should produce a similar diffraction pattern on either side of the focus when the aperture is fully open.

LET'S START TESTING

It's time to start testing the optics. This is very easy to do: just open the lens completely by removing our cardboard with a hole. The main task is to compare the appearance of the diffraction pattern given by the telescope lens on both sides of the focus. At this stage it is no longer necessary to clearly see the Airy disk, so the telescope magnification can be reduced to 8-10 times the lens diameter in centimeters.

Point the telescope at one of the bright stars, bringing its image to the center of the field of view. Bring the image out of focus until 4-8 rings are visible. Do not overdo the defocusing, otherwise the sensitivity of the test will be lost. On the other hand, if the star is not sufficiently defocused, then it will be difficult to determine the reasons that generate images of poor quality. Therefore, at this moment it is important to find a “golden mean”.

	Lens diameter	Erie mug diameter
	Millimeters	Seconds ("")
1	24.5	5.4
2,4	60	2.3
3	76.2	1.8
3.2	80	1.7
4	102	1.4
4.3	108	1.3
5	127	1.1
6	152	0.9
8	203	0.7
10	254	0.5
12.5	318	0.4
17.5	445	0.3

If you see that the diffraction pattern on either side of the focus does not look the same, then it is very likely that the optics of the telescope you are testing suffer from spherical aberration. Spherical aberration occurs when a mirror or lens is unable to converge incoming parallel rays of light to a single point. As a result, the image never becomes sharp. The following case is possible: in front of the focus (closer to the telescope lens), the rays are concentrated along the edges of the disk, and behind the focus (further from the telescope lens) - towards the center. This leads to the fact that the diffraction pattern on different sides of the focus looks different. Spherical aberration is often found in reflectors whose main mirror is poorly parabolized.

Refractor lenses, in addition to spherical aberration, also suffer from chromatic aberration, when rays of different wavelengths converge at different points. In common two-lens achromats, the orange-red and bluish-green rays converge at a slightly different point than the yellow and dark red rays. Even further away from them is the focal point for the violet rays. Fortunately, the human eye is not very sensitive to dark red and violet rays. Although, if you have observed bright planets through a large refractor, you have probably noticed a violet halo generated by chromatic aberration surrounding images of bright planets in front of the focus.

When observing a white star, for example Spica, chromatic aberration will give the following picture: in front of the focus (when about three rings are visible), the disk acquires a greenish-yellow hue, possibly with a red border. When extending the eyepiece, as the rings begin to expand again after passing the focal point, a faint red dot will appear in the center of the picture. As you move the eyepiece further out, you will again see the greenish-yellow disk, but without the red border, and a blurry purple spot will appear in the center of the picture.

Please note another possible optical error. If the color does not appear evenly, but looks like an elongated stripe in the form of a small rainbow, this may be a signal that one of the lens components is poorly centered or tilted to the optical axis. However, be careful - a similar picture can be created by the atmosphere acting like a prism if you observe the star below 45° above the horizon.

To avoid the influence of color distortions on the test results, it is recommended to use a yellow filter. This is also useful when checking a reflector, the eyepiece of which can introduce color distortions.

DON'T BLAME THE TELESCOPE

The quality of a telescope's optics is not always the main culprit for poor images. Therefore, before sinning on optics, make sure that the influence of all other factors is absent or minimized.

Atmospheric turbulence. On a night with a turbulent atmosphere, the image of the star trembles and blurs, making any optical research impossible. It is best to postpone testing the telescope until the next time when observing conditions are more favorable.

When the atmosphere is turbulent, the diffraction rings take on jagged, jagged edges with wandering spiky projections.

Air flows inside the telescope tube. Slowly rising currents of warm air inside your telescope tube can create distortions that masquerade as optical defects. In this case, the diffraction pattern, as a rule, has an elongated sector on one side or, conversely, a flat sector. To eliminate the influence of air flows that usually appear when removing a tool from a warm room, you need to wait some time so that the air temperature inside the pipe becomes equal to the ambient temperature.

Updrafts of air inside a pipe are a common but temporary problem.

Eyepiece. To test a telescope by stars, you will need a high quality eyepiece, at least a symmetrical or orthoscopic system. If a telescope test shows poor results, and even more importantly, if someone else's telescope with your eyepiece shows the same results, then suspicion should fall on the eyepiece.

Gpaza. If you are farsighted or nearsighted, it is best to remove your glasses for the test. However, if your eyes have astigmatism, then you should leave the glasses.

Telescope adjustment. Telescopes whose optics are poorly aligned will perform poorly when tested. To eliminate this drawback, telescopes are equipped with special adjustment screws that allow all system components to be aligned to the same optical axis. Alignment methods are usually described in the instructions for the telescope (see also the following article “How to align the optics of a reflecting telescope”).

If you see the same asymmetry of the rings on both sides of the focus, this is a sure sign that the telescope optics need to be adjusted

Pinched optics. Optics that are not properly mounted in the frame can cause very unusual distortions in the diffraction pattern. Most of the reflectors I tested with the main mirror pinched gave diffraction patterns of a tri- or hexagonal shape. This drawback can be eliminated by slightly loosening the screws securing the mirror to the frame.

Most often, a similar picture can be observed in a reflecting telescope, the main mirror of which is strongly compressed in the frame.

OPTICAL DEFECTS

So, we come to the most important question: does the optics of this telescope have any defects and how severe are they? Errors in optical surfaces caused by various reasons, when mixed, affect the appearance of the diffraction pattern, which may differ from the illustrations given here, which show the “pure” effect of various optical defects. More often than not, however, the influence of one of the shortcomings significantly prevails over the others, making the test scores quite unambiguous.

Spherical aberration

Above we have already considered this type of distortion, caused by the inability of a mirror or lens to bring parallel incoming rays of light to one point. As a result of spherical aberration, a dark area forms in the center of the diffraction pattern on one side of the focus. However, there is one important note to make here: be careful not to confuse spherical aberration with a shadow from the secondary mirror. The fact is that in telescopes that have a lens darkened by a secondary mirror (reflectors, meniscus telescopes), when the star is defocused, an expanding dark area appears in the center of the light spot. But unlike spherical aberration, this dark spot appears equally both in front and behind the focus.

Zone errors

Zonal errors are small depressions or low tubercles located in the form of rings on the optical surface. Optical parts made on machine tools often suffer from this drawback. In some cases, zonal errors lead to a noticeable loss of image quality. To detect the presence of this defect, you should defocus the star image a little more than for other tests. The presence of one or more weak rings in the diffraction pattern on one side of the focus will indicate the presence of zonal errors.

“Gaps” in the diffraction pattern caused by zonal errors are best seen with a highly defocused image.

Edge blockage

A special case of a zonal error is an edge collapse. It is most often caused by excessive pressure on the mirror or lens during polishing. A collapsed edge is a serious defect in optics, since a large portion of the mirror or lens seems to be out of the game.

In reflectors, edge rollover reveals its presence during testing by blurring the edge of the central disk when the eyepiece is moved closer to the lens. On the other side of the focus, the diffraction pattern turns out to be undistorted, since the roll of the edge has almost no effect here. On the contrary, a refractor has a central disk that has blurred, jagged edges when the eyepiece is behind the focus. But in a refractor, the edges of the lenses are usually “hidden” in the mounts, so the rollover of the edges in telescopes of this type affects the image quality much less than in reflectors.

When the edge of the main mirror collapses, the contrast of the diffraction pattern in front of the focus drops sharply. The postfocal diffraction pattern remains virtually undistorted.

Astigmatism

This deficiency of optical systems manifests itself in the elongation of circular diffraction rings into ellipses, the orientation of which differs by 90° on opposite sides of the focus. Therefore, the easiest way to detect astigmatism in the system is to quickly move the eyepiece in and out, passing the focal point. Moreover, weak astigmatism is easier to notice when the star is only slightly out of focus.

Once you have confirmed that there are traces of astigmatism in the diffraction pattern, do a few more checks. Often astigmatism occurs due to poor alignment of the telescope. Additionally, many people have vision astigmatism without even realizing it. To check whether your eyes are causing astigmatism, try rotating your head to see if the orientation of the diffraction ellipses changes as you rotate your head. If the orientation changes, then the eyes are to blame. Also check whether astigmatism is caused by the eyepiece by rotating the eyepiece clockwise and counterclockwise. If the ellipses also begin to rotate, then the eyepiece is to blame.

Astigmatism can also be a symptom of improperly mounted optics. If you find astigmatism in the Newtonian system reflector, then try to slightly loosen the clamps of the main and diagonal mirrors in the frame. This is unlikely to be possible with refractors, so the presence of astigmatism in this type of telescope is the reason for filing claims against the manufacturer for incorrectly installing the lenses in the frame.

Astigmatism in Newtonian system reflectors can occur due to the fact that the surface of the diagonal mirror has deviations from the plane. This can be verified by turning the main mirror 45°. See if the orientation of the ellipses has changed by the same angle. If not, then the problem lies in a poorly made secondary mirror or poor alignment of the telescope.

The semimajor axes of ellipses caused by astigmatism rotate 90° as they pass through the focal plane.

Surface roughness

Another common problem with optical surfaces is a network of bumps or depressions (ripples) that appear after rough processing with a polishing machine. In the star test, this deficiency manifests itself in a sharp decrease in the contrast between the diffraction rings, as well as in the appearance of pointed protrusions. However, do not confuse them with diffraction by diagonal mirror extensions, the projections of which are located at equal angles (usually 60° or 90°). The type of diffraction pattern caused by the surface roughness of the optics is very similar to the diffraction pattern created by atmospheric disturbances. But there is one important difference - atmospheric distortions move all the time, then disappearing, then appearing again, but optical errors remain in place.

The type of diffraction pattern caused by the surface roughness of the optics is very similar to the pattern created by atmospheric disturbances. But there is one important difference - atmospheric distortions move all the time, disappearing and reappearing, while optical errors remain in place.

WHAT TO DO, IF…

Almost all telescopes detect more or less noticeable deviations from the ideal diffraction pattern during the star test. And it's not because they are all bad tools. It's just that this method is extremely sensitive to even the smallest optical errors. It is more sensitive than the Foucault or Ronchi test. So before you judge a tool, think about this.

Let's say the worst has already happened - your instrument does not pass the star test. Don't rush to get rid of this telescope right away. It is possible that you made a mistake about something. Although the optics testing techniques described here are fairly simple, they do require some experience. Try to consult with one of your more experienced comrades. Try to test someone else's telescope (again, don't rush into categorical statements if you think you've discovered some problems with your friend's telescope - not everyone may like such “good” news).

Finally, ask yourself, how good should my telescope be? Of course, we all want top-notch equipment, but can you really expect excellent images from an inexpensive spotting scope? I have met many amateur astronomers who took great pleasure in observing the sky with telescopes that had serious optical defects. Others could leave tools whose quality was approaching perfection for a long time to gather dust in the pantry. Therefore, here I would like to repeat one old truth: the best telescope is not the one that shows ideal optical characteristics, but the one that you use most often during observations.

Translation by S. Aksyonov

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Telescope.

A telescope is an instrument designed to observe celestial bodies.

Before the telescope came along, the spotting scope was invented, created by the Dutch master John Lippershey in 1808. But the first who guessed to point the telescope into the sky was G. Galileo. In 1609, he “turned” the spotting scope into a telescope, and this telescope became a spotting scope with 3x magnification. In the same year, Galileo built a telescope with 8x magnification. Later, Galileo was able to create a telescope that gave a magnification of 32x. Galileo called the invention "perspicillum" (directly translated into Russian - "glass"). The term "telescope" was coined in 1611 by the Greek mathematician Giovanni Demisiani..

There are different types of telescopes:
1. gamma telescopes;
2. radio telescopes;
3. X-ray telescopes;
4. optical telescopes.

1. Gamma-ray telescopes.
These are telescopes that use gamma waves to explore space. Astronomical gamma rays appear in
studies of astronomical objects with a short wavelength of the electromagnetic spectrum. Most gamma ray sources are actually gamma ray burst sources, which emit only gamma rays for a short period of time ranging from a few milliseconds to a thousand seconds before dissipating into space. Gamma-ray telescopes study pulsars, neutron stars and black hole candidates in active galactic nuclei.

2. Radio telescopes
Their purpose is to receive radio emissions from celestial objects and study their characteristics: coordinates, radiation intensity, etc. In order to receive a clear signal from objects, radio telescopes should preferably be located far from the main populated areas in order to minimize electromagnetic interference from broadcast radio stations, television, radars and other emitting devices. Placing a radio observatory in a valley or lowland can protect it even better from the influence of man-made electromagnetic noise. There are amateur astronomers who use radio telescopes. Most often these are telescopes made by hand.

3. X-ray telescopes.
Designed for observing distant objects in the X-ray spectrum. To operate properly, they must be raised above the Earth's atmosphere, which is opaque to X-rays. Therefore, telescopes are placed in Earth orbits.

4. Optical telescopes.
What is an optical telescope? This is a pipe mounted on a mount, which is equipped with various axes to point the pipe at the object of observation. The telescope has a lens and an eyepiece. The rear focal plane of the lens is aligned with the front focal plane of the eyepiece. Instead of an eyepiece, photographic film or a matrix radiation receiver can be placed in the focal plane of the lens. In this case, the telescope lens, from an optical point of view, is a photographic lens. The telescope is focused using a focusing device.

According to their optical design, telescopes of this type are divided into:

• Lens (refractors) - an optical telescope that uses a system to collect light
  lenses The operation of such telescopes is due to the phenomenon of refraction (refraction). Refractors contain two main components: a lens objective and an eyepiece.
• Mirror (reflector) - an optical telescope that uses mirrors as light-collecting elements.
• Mirror-lens telescopes (catadioptric) are a telescope in which the image is formed by a complex lens containing both mirrors and lenses.

You have decided to purchase a telescope for your child so that he can explore the world and explore the secrets of the Universe. Or you wanted to try your hand at astrophotography. For each purpose, you need to choose a special device, since there is no ideal telescope that could simultaneously help you in different astronomical observations. Next, we will look at the types of telescopes according to their optical design.

How refractors work

The front part of the tube of such a device has a lens that acts as a lens. If we compare the refractor with other systems, it is longer. The price of the device is determined by the quality of the lens and its magnification capabilities.

The disadvantage of refractors is the presence of aberration, which leaves halos over objects of contemplation and distorts the image. To prevent a negative effect, modern lenses, smart ratios, and low-dispersion glass are used. Such telescopes are ideal for observing different planets, stars and even the Moon.

There are three different types of refracting telescopes - ED refractors, apochromats, and achromats.

The lens of achromatic devices consists of two lenses, which consist of a flint and a crown. The different composition and air gap between the lenses helps prevent distortion.

Today you can buy long-focus (aperture 1/10-1/12) and short-focus (1/5-1/6). The latter are easy to transport due to their compact and lightweight appearance. These telescopes are often mounted on a stand and view comets, nebulae and the Milky Way.

ED refractors and apochromats are presented in the expensive segment. They provide a more detailed image of objects that are located in deep space.

ED refractors are built in the same way as apochromats, but instead of crown and flint, they use a different material for making lenses - low dispersion ED glass, which helps to see planets and stars better without distortion. The high cost of such a telescope is justified by the strength of the mechanical components and suitability for astrophotography.

Apochromats, according to reviews from experienced astronomers, produce the most accurate images of space objects. The chromatic aberration of the telescope is corrected in the wavelengths of the spectrum. The design of apochromatic refractor lenses can consist of 3-5 different lenses made from the most expensive optical fluorite glass.

Attention! Apochromats are great for experienced astrophotographers who want to observe perfect images of stars, satellites and planets. Therefore they are expensive.

Choosing a reflector

The reflector lens is a concave mirror at the bottom of the tube. It has become much cheaper and easier for manufacturers to make mirrors, so reflector-type telescopes cost less than refractors.

The thinnest layer of mirror reflection requires careful handling of the telescope - do not expose it to sudden changes in temperature and store it in a case so that moisture does not condense on the surface of the mirrors.

Attention! There are many lens diameters - from 76 to 250 mm. The low price of a device does not mean that it works worse than others. It is designed for contemplating distant star clusters and has a good aperture ratio.

The most famous and inexpensive reflecting telescopes are considered to be instruments operating according to the Newtonian system. In it, light hitting a spherical mirror is refracted on a secondary flat one. You can purchase such devices with a diameter from 76 to 400 mm.

There are also reflectors that perform their functions according to the Doll-Kerkem, Cassegrain, Ritchie-Chretien system. They differ in the concavity of the mirror lenses and their placement in the lens. Such devices are presented in mass production, but are subject to aberrations. Ideal for astrophotography and optical observations of planets.

Telescopes based on the Maksutov-Cassegrain and Schmidt-Cassegrain systems

Catadioptrics (the general name for telescopes in this category) embodied the dream of all amateur astronomers - combining the advantages of lens and mirror instruments for observing stars and planets.

The most popular are the Schmidt-Kassergen system devices. They are light, compact, do not require a rigid tripod and produce high-quality images.

To correct the possibility of distortion in the visibility of a celestial object, manufacturers have installed correction plates and lenses in these systems.

Choosing the right mount

During long-term observation of stars and planets, the need for a telescope stand arises - your hands get tired and begin to tremble, which leads to image distortion.

There are several types of stands:

• The equatorial one is designed for precise observations, astrophotography, and allows you to set coordinates;
• Azimuthal - more convenient to use reflectors for children;
• The Dobsonian system is simple and often comes with large reflectors.

The telescope support will become a reliable assistant for you and there is no need to skimp on it.

The ideal device for your purposes

In accordance with the wishes of the novice astronomer or experienced photographer of celestial objects, we have divided telescopes into categories:

• First. A refractor-type telescope of 70-90 mm or Newtonian reflectors with a lens size of 120 mm will suit a non-picky user.
• For a child. When choosing a telescope for a child, you don’t have to worry about image accuracy and high quality. For this purpose, you can buy a reflector or refractor from an inexpensive segment.
• Universal. Manufacturers offer this type of telescope for people who want to observe objects on Earth and in space. Buy a 120 mm refractor, 140 mm reflector, 110 mm Maksutov-Cassegrain.
• To photograph astronomical bodies, choose telescopes with a high lens rating. It is also necessary to have an equatorial type mount with electric drives.
• Contemplation of the planets. A bright image can be obtained using a 150 mm refractor.
• For examining objects in deep space, 240 mm reflectors with an equatorial support or a Dobsonian tripod are suitable.
• For frequent movements, refractors with a short focus and working according to the Maksutov-Cassegrain system are suitable. They are light and small and will not create inconvenience during transportation.

When buying a telescope for a novice observer of stars and nebulae, you do not need to pay a lot of money; even the simplest device with minimal magnification and the presence of aberration will be a gift for him. And in the near future, when he becomes a professional astronomer, he can think about purchasing more expensive models.

How to choose a telescope - video