How does a telescope work? How are telescopes of various optical schemes constructed? Telescope types and principle of operation

Optical telescope- a tool for collecting and focusing electromagnetic radiation optical range. The telescope increases the brightness and apparent angular size of the observed object. Simply put, a telescope allows you to study finer details of an object of observation by increasing the amount of incoming light. Through a telescope you can observe with your eye (visual observations), and you can also take photographs or videos. To determine the characteristics of a telescope, the main parameters are the diameter (aperture) and focal length of the lens, as well as the focal length and field of view of the eyepiece. The telescope is mounted on a mount, which makes the observation process more comfortable. The mount makes it possible to simplify the process of pointing and tracking an observation object.

According to the optical design, telescopes are divided into:

Lens (refractors or diopter) - a lens or lens system is used as a lens.
- Mirror (reflector or cataptric) - a concave mirror is used as a lens.
- Mirror-lens telescopes (catadioptric) - a spherical mirror is used as a lens, and a lens, lens system or meniscus serves to compensate for aberrations.

The first astronomer who managed to build a telescope was the Italian Galileo Galilei. The created telescope was of modest size, tube length 1245 mm, lens diameter 53 mm, eyepiece 25 diopters. Its optical design was not perfect, and the magnification was only 30 times. But with all its shortcomings, having more than modest dimensions, the telescope made it possible to make a number of remarkable discoveries: craters and mountains on the Moon, four satellites of Jupiter, sunspots on the Sun, phase changes of Venus, strange “appendages” of Saturn (the ring of Saturn, which was later discovered and described by Huygens), the light in the Milky Way consists of stars.

A portrait of Galileo, a broken lens from the first telescope in the center of the vignette and his telescopes on a museum stand, stored in the Museum of the History of Science (Florence).

Classic optical schemes.

Galileo's scheme.

In 1609, Italian Galileo Galilei built the first telescope. His objective was one converging lens, and the eyepiece was a diverging lens, as a result of which the image was not inverted (Earthly). The main disadvantages of this optical design are very strong chromatic aberration and a small field of view. To this day, such a scheme is still used in theater binoculars and home-made amateur telescopes.

Kepler scheme

In 1611, German astronomer Johannes Kepler improved Galileo's telescope. He replaced the diverging lens in the eyepiece with a converging one. Its changes made it possible to increase the field of view and eye relief. This optical design produces an inverted real image. In fact, all subsequent refracting telescopes are Kepler tubes. The disadvantages of the system include strong chromatic aberration, which, before the creation of an achromatic lens, was eliminated by reducing the relative aperture of the telescope.

Newton's scheme

In 1667, English astronomer Isaac Newton proposed a design in which light falls on the main mirror, and then a flat diagonal mirror located near the focus deflects the light beam outside the tube. The main mirror has a parabolic shape, and in the case where the relative aperture is not too large, the shape of the mirror is spherical.

Gregory's scheme

In 1663, Scottish astronomer James Gregory proposed the following scheme in his book Optica Promota. The concave parabolic primary mirror reflects light onto the concave elliptical secondary mirror, after which the light passes through an opening in the primary mirror and enters the eyepiece. The distance between the mirrors is greater than the focal length of the main mirror, so the image is upright (as opposed to inverted in a Newtonian telescope). The secondary mirror provides relatively high magnification by extending the focal length.

Cassegrain scheme

In 1672, the Frenchman Laurent Cassegrain proposed a design for a two-mirror telescope lens. The concave primary mirror (originally parabolic) reflects light onto a smaller, convex, hyperbolic secondary mirror, which then enters the eyepiece. According to Maksutov’s classification, the scheme belongs to the so-called prefocal extension - that is, the secondary mirror is located between the main mirror and its focus and the total focal length of the lens is greater than that of the main one. The lens, with the same diameter and focal length, has almost half the tube length and slightly less shielding than Gregory's. The system is non-aplanatic, that is, not free from the aberration of coma. It has many mirror modifications, including aplanatic Ritchie-Chretien, with a spherical surface shape of the secondary (Doll-Kirham) or primary mirror, and mirror-lens ones.

Maksutov-Cassegrain scheme

In 1941, the Soviet scientist, optician D. D. Maksutov found that the spherical aberration of a spherical mirror can be compensated by a meniscus of large curvature. Having found the right distance between the meniscus and the mirror, Maksutov managed to get rid of coma and astigmatism. The curvature of the field, as in the Schmidt camera, can be eliminated by installing a plane-convex lens near the focal plane - the so-called Piazzi-Smith lens. By modifying the Cassegrain system, Maksutov created one of the most common systems in astronomy.

Ritchie-Chrétien scheme

In the early 1910s, American and French astronomers George Ritchie and Henri Chrétien invented the optical design of a refracting telescope, a variation of the Cassegrain system. A feature of the Ritchie-Chretien system that distinguishes it from most other variants of the Cassegrain system is the absence of third-order coma and spherical aberration. On the other hand, high-angle astigmatism and field curvature are large; the latter, however, can be corrected with a simple two-lens field corrector. Like other cassegrains, it has a short body, a secondary mirror, which in the case of the Ritchie-Chretien system is hyperbolic and prevents the appearance of coma and promotes a wide field. This scheme is the most common in scientific telescopes. The most famous telescope using the Ritchie-Chrétien design is the Hubble Space Telescope.

Since the creation of the first telescope in 1611, astronomers have made discoveries by observing visually. As science progressed, observation methods also progressed. After 1920, photographic plates became the image receiver. Although the eye is the most complex organ, it is significantly inferior in sensitivity to photographic plates.

The next breakthrough was the creation of the CCD matrix after 1980. They were significantly superior in sensitivity to photographic plates and were much more convenient to use. In all modern telescopes The image receivers are CCD matrices. CCD matrix or CCD matrix is a specialized analog integrated circuit consisting of light-sensitive photodiodes, made on the basis of silicon, using CCD technology - charge-coupled devices. The resulting images are processed digitally on a computer. To obtain clear images without digital noise, the matrix is cooled to -130°C.

The largest telescope in Russia is BTA (“Large Azimuth Telescope”).

The main mirror (MS) has the shape of a paraboloid of rotation and a focal length of 24 m. The diameter of the mirror is 605 cm. The mass of the main mirror is 42 tons. The telescope weighs 850 tons. The height of the telescope is 42 m. The height of the tower is 53 m. The diameter of the primary focus cabin is 2 m. There are replaceable optical instruments here, as well as a drive mechanism for moving the lens corrector and the hyperbolic secondary mirror. Laboratory tests show that 90% of the energy is concentrated in a circle with a diameter of 0.8". The diameter of the image is determined by the microclimate in the tower room, as well as the temperature of the mirror. Under favorable conditions (small temperature difference between the main zone, the air in the dome room and next to the tower), the size of the stars images are limited by atmospheric turbulence. The optical design of the BTA allows for observations at the primary focus (aperture f/4) and at two Nesmith focuses (aperture f/30). nights of observations using equipment installed at different focal points of the telescope.

At the moment, the largest telescope built is Very Large Telescope VLT (very large telescope).

The telescope complex was built by the European Southern Observatory (ESO). This is a complex of four separate 8.2-meter and four auxiliary 1.8-meter optical telescopes, combined into one system. The complex is located in the Republic of Chile on Mount Cerro Paranal, 2635 meters above sea level. The main 8.2 meter telescopes are housed in compact, temperature-controlled towers that rotate synchronously with the telescopes themselves. This arrangement minimizes any distorting effects of external conditions during observations, such as optical distortions introduced by air turbulence in the telescope tube, which usually occurs due to changes in temperature and wind. The first of the Primary Telescopes, Antu, began regular scientific observations on April 1, 1999. Currently, all four Primary and all four Auxiliary Telescopes are operational. VLT Core Telescope Towers: height 2850 cm, diameter 2900 cm. Although four 8.2 meter Core Telescopes can be used in combination to form a VLTI, they are primarily used for individual observations; in interferometric mode they operate only a limited number of nights a year. But thanks to four smaller, dedicated Auxiliary Telescopes (ATs), VLTI can operate every night.

The very large telescope is equipped with a large arsenal of imaging receivers, allowing it to observe wavelengths ranging from near ultraviolet to mid-infrared. The adaptive optics system installed on the telescope almost completely eliminates the influence of a turbulent atmosphere in the infrared range. The resulting images in this range are clearer than those obtained by the Hubble telescope.

Telescope structure

In the 20th century, astronomy made many steps in studying our Universe, but these steps would have been impossible without the use of such complex instruments as telescopes, the history of which goes back hundreds of years. The evolution of the telescope took place in several stages, and I will try to talk about them.

Since ancient times, humanity has been drawn to find out what is there, in the sky, beyond the Earth and the invisible to the human eye. The greatest scientists of antiquity, such as Leonardo da Vinci, Galileo Galilei, attempted to create a device that would allow one to look into the depths of space and lift the veil of mystery of the Universe. Since then, many discoveries have occurred in the field of astronomy and astrophysics. Every person knows what a telescope is, but not everyone knows how long ago and by whom the first telescope was invented, and how it was designed.

A telescope is a device designed for observing celestial bodies.

In particular, a telescope refers to an optical telescopic system not necessarily used for astronomical purposes.

There are telescopes for all ranges of the electromagnetic spectrum:

optical telescopes

radio telescopes

X-ray telescopes

gamma-ray telescopes

Optical telescopes

A telescope is a tube (solid, frame or truss) mounted on a mount equipped with axes for pointing at and tracking the object of observation. A visual 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 the point of view of optics, is a photographic lens. The telescope is focused using a focuser (focused device). telescope space astronomy

According to their optical design, most telescopes are divided into:

Lens (refractors or diopter) - a lens or lens system is used as a lens.

Mirror (reflector or catoptric) - a concave mirror is used as a lens.

Mirror-lens telescopes (catadioptric) - a spherical mirror is used as a lens, and a lens, lens system or meniscus serves to compensate for aberrations.

Radio telescopes

Radio telescopes are used to study space objects in the radio range. The main elements of radio telescopes are a receiving antenna and a radiometer - a sensitive radio receiver, frequency tunable, 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. In the long-wave region (meter range; tens and hundreds of megahertz), telescopes are used that are composed of a large number (tens, hundreds or even thousands) of elementary receivers, usually dipoles. For shorter waves (decimeter and centimeter range; tens of gigahertz), semi- or fully rotating parabolic antennas are used. In addition, to increase the resolution of telescopes, they are combined into interferometers. When several single telescopes located in different parts of the globe are combined into a single network, 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 also planned to be used as one of the elements of the giant interferometer.

X-ray telescope

An X-ray telescope is a telescope designed to observe distant objects in the X-ray spectrum. To operate such telescopes typically require them to be raised above the Earth's atmosphere, which is opaque to X-rays. Therefore, telescopes are placed on high-altitude rockets or satellites.

Optical design

Due to their high energy, X-ray quanta are practically not refracted in matter (hence, it is difficult to make lenses) and are not reflected at any angle of incidence except the shallowest (about 90 degrees).

X-ray telescopes can use several methods to focus beams. The most commonly used telescopes are Voltaire telescopes (with grazing incidence mirrors), aperture coding, and modulation (oscillating) collimators.

The limited capabilities of X-ray optics result in a narrower field of view compared to telescopes operating in the UV and visible light ranges.

The invention of the first telescope is often attributed to Hans Lipperschlei of Holland, 1570-1619, but he was almost certainly not the discoverer. Most likely, his merit is that he was the first to make the new telescope device popular and in demand. It was also he who applied for a patent in 1608 for a pair of lenses placed in a tube. He called the device a spyglass. However, his patent was rejected because his device seemed too simple.

Long before him, Thomas Digges, an astronomer, tried to magnify stars in 1450 using a convex lens and a concave mirror. However, he did not have the patience to finalize the device, and the half-invention was soon conveniently forgotten. Today Digges is remembered for his description of the heliocentric system.

By the end of 1609, small telescopes, thanks to Lipperschlei, became common throughout France and Italy. In August 1609, Thomas Harriot refined and improved the invention, allowing astronomers to view craters and mountains on the Moon.

The big breakthrough came when Italian mathematician Galileo Galilei learned of a Dutchman's attempt to patent a lens tube. Inspired by the discovery, Halley decided to make such a device for himself. In August 1609, it was Galileo who made the world's first full-fledged telescope. At first, it was just a spotting scope - a combination spectacle lenses, today it would be called a refractor. Before Galileo, most likely, few people thought of using this entertainment tube for the benefit of astronomy. Thanks to the device, Galileo himself discovered mountains and craters on the Moon, proved the sphericity of the Moon, discovered four satellites of Jupiter, the rings of Saturn and made many other useful discoveries.

To today's person, the Galileo telescope will not seem special; any ten-year-old child could easily build a much better instrument using modern lenses. But the Galileo telescope was the only real working telescope of the day with 20x magnification, but with a small field of view, a slightly blurry image and other shortcomings. It was Galileo who opened the age of the refractor in astronomy - the 17th century.

Time and the development of science made it possible to create more powerful telescopes that made it possible to see much more. Astronomers began to use lenses with longer focal lengths. The telescopes themselves turned into large, heavy pipes in size and, of course, were not convenient to use. Then tripods were invented for them. Telescopes were gradually improved and refined. However, its maximum diameter did not exceed a few centimeters - it was not possible to produce large lenses.

By 1656, Christian Huyens made a telescope that magnified observed objects 100 times; its size was more than 7 meters, with an aperture of about 150 mm. This telescope is already considered to be at the level of today's amateur telescopes for beginners. By the 1670s, a 45-meter telescope had already been built, which further magnified objects and provided a wider angle of view.

But even ordinary wind could serve as an obstacle to obtaining a clear and high-quality image. The telescope began to grow in length. The discoverers, trying to get the most out of this device, relied on the optical law they discovered - a decrease in the chromatic aberration of a lens occurs with an increase in its focal length. To eliminate chromatic interference, researchers made telescopes of incredible lengths. These pipes, which were then called telescopes, reached 70 meters in length and caused a lot of inconvenience in working with them and setting them up. The shortcomings of refractors forced great minds to look for solutions to improve telescopes. Answer and new way was found: the collection and focusing of rays began to be carried out using a concave mirror. The refractor was reborn into a reflector, completely freed from chromaticism.

This merit belongs entirely to Isaac Newton, it was he who was able to give new life to telescopes with the help of a mirror. His first reflector had a diameter of only four centimeters. And he made the first mirror for a telescope with a diameter of 30 mm from an alloy of copper, tin and arsenic in 1704. The image became clear. By the way, his first telescope is still carefully preserved in the Astronomical Museum in London.

But also for a long time opticians were unable to make full-fledged mirrors for reflectors. The year of birth of a new type of telescope is considered to be 1720, when the British built the first functional reflector with a diameter of 15 centimeters. It was a breakthrough. In Europe, there is a demand for portable, almost compact telescopes two meters long. They began to forget about the 40-meter refractor tubes.

The two-mirror system in the telescope was proposed by the Frenchman Cassegrain. Cassegrain was unable to fully implement his idea due to the lack of technical ability to invent the necessary mirrors, but today his drawings have been implemented. It was the Newtonian and Cassegrain telescopes that are considered the first “modern” telescopes, invented at the end of the 19th century. By the way, the Hubble Space Telescope works exactly on the principle of the Cassegrain telescope. And Newton's fundamental principle using a single concave mirror has been used at the Special Astrophysical Observatory in Russia since 1974. The heyday of refractor astronomy occurred in the 19th century, when the diameter of achromatic lenses gradually increased. If in 1824 the diameter was still 24 centimeters, then in 1866 its size doubled, in 1885 the diameter became 76 centimeters (Pulkovo Observatory in Russia), and by 1897 the Ierka refractor was invented. It can be calculated that over 75 years the lens has increased at the rate of one centimeter per year.

By the end of the 18th century, compact, convenient telescopes came to replace bulky reflectors. Metal mirrors also turned out to be not very practical - they are expensive to produce and also fade over time. By 1758, with the invention of two new types of glass: light - crown and heavy - flint, it became possible to create two-lens lenses. This was successfully taken advantage of by the scientist J. Dollond, who made a two-lens lens, later called the Dollond lens.

After the invention of achromatic lenses, the victory of the refractor was absolute; all that remained was to improve lens telescopes. They forgot about concave mirrors. They were brought back to life by the hands of amateur astronomers. William Herschel, English musician who discovered the planet Uranus in 1781. His discovery has not been equal in astronomy since ancient times. Moreover, Uranus was discovered using a small homemade reflector. The success prompted Herschel to begin making larger reflectors. Herschel himself fused mirrors from copper and tin in his workshop. The main work of his life was a large telescope with a mirror with a diameter of 122 cm. This is the diameter of his largest telescope. The discoveries were not long in coming; thanks to this telescope, Herschel discovered the sixth and seventh satellites of the planet Saturn. Another, no less famous, amateur astronomer, English landowner Lord Ross, invented a reflector with a mirror with a diameter of 182 centimeters. Thanks to the telescope, he discovered a number of unknown spiral nebulae. The Herschel and Ross telescopes had many disadvantages. Mirror metal lenses turned out to be too heavy, reflected only a small part of the light falling on them and became dim. A new perfect material for mirrors was required. This material turned out to be glass. French physicist Leon Foucault tried to insert a mirror made of silvered glass into a reflector in 1856. And the experience was a success. Already in the 90s, an amateur astronomer from England built a reflector for photographic observations with a glass mirror 152 centimeters in diameter. Another breakthrough in telescope construction was obvious.

This breakthrough could not have happened without the participation of Russian scientists. I'M IN. Bruce became famous for developing special metal mirrors for telescopes. Lomonosov and Herschel, independently of each other, completely invented new design telescope in which the main mirror tilts without a secondary one, thereby reducing light loss.

The German optician Fraunhofer put the production and quality of lenses on the conveyor belt. And today at the Tartu Observatory there is a telescope with a intact, working Fraunhofer lens. But the refractors of the German optician were also not without a flaw - chromatism.

It was only towards the end of the 19th century that a new method for producing lenses was invented. Glass surfaces began to be treated with a silver film, which was applied to a glass mirror by exposing grape sugar to silver nitrate salts. These fundamentally new lenses reflected up to 95% of the light, in contrast to the old bronze lenses, which reflected only 60% of the light. L. Foucault created reflectors with parabolic mirrors, changing the shape of the surface of the mirrors. In the late 19th century, Crossley, an amateur astronomer, turned his attention to aluminum mirrors. The concave glass parabolic mirror with a diameter of 91 cm that he purchased was immediately inserted into the telescope. Today, telescopes with such huge mirrors are installed in modern observatories. While the growth of the refractor slowed, development of the reflecting telescope gained momentum. From 1908 to 1935, various observatories around the world built more than one and a half dozen reflectors with a lens larger than that of Yerk. The largest telescope is installed at the Mount Wilson Observatory, its diameter is 256 centimeters. And even this limit will soon be doubled. An American giant reflector was installed in California; today it is more than fifteen years old.

More than 30 years ago in 1976, USSR scientists built a 6-meter BTA telescope - the Large Azimuthal Telescope. Until the end of the 20th century, the BTA was considered the world's largest telescope. The inventors of the BTA were innovators in original technical solutions, such as a computer-guided alt-azimuth installation. Today, these innovations are used in almost all giant telescopes. At the beginning of the 21st century, the BTA was pushed into the second ten large telescopes in the world. And the gradual degradation of the mirror over time - today its quality has fallen by 30% of its original value - turns it only into a historical monument to science.

The new generation of telescopes includes two large 10-meter twin telescopes KECK I and KECK II for optical infrared observations. They were installed in 1994 and 1996 in the USA. They were collected thanks to the help of the W. Keck Foundation, after which they are named. He provided more than $140,000 for their construction. These telescopes are the size of an eight-story building and weigh more than 300 tons each, but they operate with the highest precision. The operating principle is a main mirror with a diameter of 10 meters, consisting of 36 hexagonal segments, working as one reflective mirror. These telescopes are installed in one of the optimal places on Earth for astronomical observations - in Hawaii, on the slope of the extinct volcano Manua Kea 4,200 m high. By 2002, these two telescopes, located at a distance of 85 m from each other, began to operate in interferometer mode, giving the same angular resolution as an 85 meter telescope. The history of the telescope has come a long way - from Italian glassmakers to modern giant satellite telescopes. Modern large observatories have long been computerized. However, amateur telescopes and many devices such as Hubble are still based on the operating principles invented by Galileo.

Application

Modern telescopes allow astronomers to “look” far beyond the boundaries of our Universe. To accurately point devices at an object, complex software algorithms are used, which have unexpectedly become very useful for oncologists.

When observing distant galaxies and during the search for new celestial bodies, scientists have to calculate complex trajectories of space objects so that at a certain moment in time the telescope “looks” at exactly that part of the sky where a distant planet, comet or asteroid will be most clearly visible.

Such calculations are made using sophisticated, specially written programs for computers that control telescopes.

And British scientists involved in oncology problems, in particular the study of breast cancer, have more than successfully used “astronomical” computer programs to analyze samples of breast cancer tumors.

Researchers at the University of Cambridge studied 2,000 cancer samples to improve the technique, the so-called personalization of cancer treatment. This technique requires precise knowledge maximum number individual characteristics of the tumor in a particular patient to select the most effective chemotherapy drugs.

Using conventional methods, scientists would have to spend at least a week analyzing 2,000 samples - but the use of “astronomical” programs made it possible to complete this work in less than 1 day.

To make adjustments to the program and its maximum adaptation for the needs of oncology, Cambridge scientists plan to soon analyze 20,000 samples of breast tumors obtained from patients from different countries Europe.

The principle of a telescope is not to magnify objects, but to collect light. The larger the size of the main light-gathering element - a lens or mirror, the more light will enter it. Importantly, it is the total amount of light collected that ultimately determines the level of detail seen - be it a distant landscape or the rings of Saturn. While magnification, or power, for a telescope is important, it is not critical to achieving the level of detail.

Telescopes are constantly changing and improving, but the principle of operation remains the same.

The telescope collects and concentrates light

The larger the convex lens or concave mirror, the more light enters it. And the more light enters, the more distant objects it allows you to see. The human eye has its own convex lens (lens), but this lens is very small, so it collects quite a bit of light. A telescope allows you to see more precisely because its mirror is capable of collecting more light than the human eye.

The telescope focuses light rays and creates an image

In order to create a clear image, the lenses and mirrors of the telescope collect the captured rays into one point - the focus. If the light is not concentrated into one point, the image will be blurry.

Types of telescopes

Telescopes can be divided according to the way they work with light into “lens”, “mirror” and combined - mirror-lens telescopes.

Refractors are refracting telescopes. The light in such a telescope is collected using a biconvex lens (in fact, it is the lens of the telescope). Among amateur instruments, the most common achromats are usually two-lens ones, but there are also more complex ones. An achromatic refractor consists of two lenses - a collecting and a diverging one, which makes it possible to compensate for spherical and chromatic aberrations - in other words, distortions in the flow of light when passing through the lens.

A little history:

Galileo's refractor (created in 1609) used two lenses to collect as much starlight as possible. and allow the human eye to see it. Light passing through a spherical mirror forms an image. Galileo's spherical lens makes the picture blurry. In addition, such a lens decomposes light into color components, which is why a blurry colored area is formed around the luminous object. Therefore, the convex spherical lens collects starlight, and the concave lens following it turns the collected light rays back into parallel ones, which makes it possible to restore clarity and clarity to the observed image.

Keppler Refractor (1611)

Any spherical lens refracts light rays, defocusing them and blurring the picture. A spherical Keppler lens has less curvature and a longer focal length than a Galilean lens. Therefore, the focusing points of rays passing through such a lens are closer to each other, which makes it possible to reduce, but not completely eliminate, image distortions. In fact, Keppler himself did not create such a telescope, but the improvements he proposed had a strong influence on further development refractors.

Achromatic refractor

The achromatic refractor is based on the Keppler telescope, but instead of one spherical lens it uses two lenses of different curvatures. Light passing through these two lenses is focused at one point, i.e. This method avoids both chromatic and spherical aberration.

Telescope Sturman F70076
A simple and lightweight refractor for beginners with a 50mm objective lens. Magnification - 18*,27*,60*,90*. It is equipped with two eyepieces - 6 mm and 20 mm. Can be used as a pipe as it does not reverse the image. On an azimuth bracket.
>Konus KJ-7 telescope
60 mm long-focus refractor telescope on a German (equatorial) mount. Maximum magnification - 120x. Suitable for children and beginning astronomers.
Telescope MEADE NGC 70/700mm AZ
A classic refractor with a diameter of 70 mm and a maximum useful magnification of up to 250*. Comes with three eyepieces, prism and mount. Allows you to observe almost all the planets of the Solar System and faint stars up to magnitude 11.3.
Telescope Synta Skywatcher 607AZ2
A classic refractor on an AZ-2 azimuth mount on an aluminum tripod and the ability to micro-scale the telescope in height. Lens diameter 60 mm, maximum magnification 120 times, penetrating power 11 (magnitudes). Weight 5 kg.
Telescope Synta Skywatcher 1025AZ3
A lightweight refractor with an alt-azimuth mount AZ-3 on an aluminum tripod with micrometer guidance of the telescope in both axes. Can be used as a telephoto lens for most DSLR cameras to photograph distant objects. Lens diameter 100 mm, focal length 500 mm, penetrating power 12 (magnitudes). Weight 14 kg.

Reflector is any telescope whose lens consists only of mirrors. Reflectors are reflective telescopes, and the image in such telescopes appears on the other side of the optical system than in refractors.

A little history

Gregory reflecting telescope (1663)

James Gregory introduced absolutely new technology in the manufacture of telescopes, having invented a telescope with a parabolic primary mirror. The image that can be observed through such a telescope is free from both spherical and chromatic aberrations.

Newton's reflector (1668)

Newton used a metal primary mirror to collect light and a subsequent guide mirror that redirected the light rays to the eyepiece. In this way, it was possible to cope with chromatic aberration - because instead of lenses, this telescope uses mirrors. But the picture still turned out blurry due to the spherical curvature of the mirror.

Until now, a telescope made according to Newton’s scheme is often called a reflector. Unfortunately, it is not free from aberrations. A little to the side of the axis, coma (non-isoplanatism) begins to appear - an aberration associated with the uneven magnification of different annular zones of the aperture. Coma leads to the fact that the scattering spot looks like a projection of a cone - the sharp and brightest part towards the center of the field of view, dull and rounded away from the center. The size of the scattering spot is proportional to the distance from the center of the field of view and is proportional to the square of the aperture diameter. Therefore, the manifestation of coma is especially strong in the so-called “fast” (high-aperture) Newtons at the edge of the field of view.

Newtonian telescopes are still very popular today: they are very simple and cheap to manufacture, which means their average prices are much lower than for corresponding refractors. But the design itself imposes some limitations on such a telescope: distortions of the rays passing through the diagonal mirror noticeably worsen the resolution of such a telescope, and as the diameter of the lens increases, the length of the tube increases proportionally. As a result, the telescope becomes too large, and the field of view with a long tube becomes smaller. Actually, reflectors with a diameter greater than 15 cm are practically not produced, because... Such devices will have more disadvantages than advantages.

Telescope Synta Skywatcher 1309EQ2
Reflector with a lens diameter of 130 mm on an equatorial mount. Maximum magnification 260. Insight 13.3
Telescope F800203M STURMAN
Reflector with a lens diameter of 200 mm on an equatorial mount. Comes with two eyepieces, moon filter, tripod and viewfinders.
Meade Newton 6 LXD-75 f/5 telescope with EC remote control
A classic Newtonian reflector with a lens diameter of 150 mm and a useful magnification of up to 400x. A telescope for astronomy enthusiasts who value a large light diameter and high aperture ratio. An electronically driven mount with clock tracking allows for long exposure astrophotography.

Mirror-lens(catadioptric) telescopes use both lenses and mirrors to achieve superb high-resolution image quality from very short, portable optical tubes.

Telescope parameters

Diameter and magnification

When choosing a telescope, it is important to know about the lens diameter, resolution, magnification, and quality of construction and components.

The amount of light collected by a telescope directly depends on diameter(D) the primary mirror or lens. The amount of light passing through the lens is proportional to its area.

In addition to the diameter, the size of the lens is important for its characteristics. relative hole(A), equal to the ratio of the diameter to the focal length (also called aperture).

Relative Focus is called the reciprocal of the relative aperture.

Permission- this is the ability to display details - i.e. The higher the resolution, the better the image. A high-resolution telescope will be able to separate two distant, close objects, while a low-resolution telescope will only see one mixed object. Stars are point sources of light, so they are difficult to observe, and in a telescope you can only see a diffraction image of the star in the form of a disk with a ring of light around it. Officially, the maximum resolution of a visual telescope is the minimum angular gap between a pair of stars of equal brightness when they are still visible at sufficient magnification and there is no interference from the atmosphere separately. This value for good instruments is approximately equal to 120/D arcseconds, where D is the telescope aperture (diameter) in mm.

Increases telescope should lie in the range from D/7 to 1.5D, where D is the diameter of the telescope lens aperture. That is, for a tube with a diameter of 100 mm, eyepieces must be selected so that they provide magnifications from 15x to 150x.

At a magnification numerically equal to the diameter of the lens, expressed in millimeters, the first signs of a diffraction pattern appear, and further increases in magnification will only worsen the image quality, making it impossible to distinguish fine details. In addition, it is worth remembering about telescope shake, atmospheric turbulence, etc. Therefore, when observing the Moon and planets, magnifications exceeding 1.4D - 1.7D are usually not used. In any case, a good instrument should be able to “pull out” up to 1.5D without significantly degrading image quality. Refractors cope best with this, and reflectors with their central shielding can no longer work reliably at such magnifications, therefore, it is not advisable to use them for observing the Moon and planets.

The upper limit of rational magnification is determined empirically and is related to the influence of diffraction phenomena (as magnification increases, the size of the telescope's exit pupil, its exit aperture, decreases). It turned out that the highest resolution is achieved with exit pupils of less than 0.7 mm and further increase in magnification does not lead to an increase in the number of details. On the contrary, a loose, cloudy and dim image creates the illusion of reduced detail. Large magnifications of 1.5D make sense as they are more comfortable, especially for people with visual impairments and only for bright, contrasting objects.

The lower limit of a reasonable magnification range is determined by the fact that the ratio of the lens diameter to the exit pupil diameter (i.e., the diameter of the light beam emerging from the eyepiece) is equal to the ratio of their focal lengths, i.e. increase. If the diameter of the beam emerging from the eyepiece exceeds the diameter of the observer's pupil, some of the rays will be cut off, and the observer's eye will see less light - and a smaller part of the image.

Thus, the following series of recommended magnifications emerges: 2D, 1.4D, 1D, 0.7D, D/7. Magnification of D/2..D/3 is useful for observing normal-sized clusters and dim nebulous objects.

Mounts

Telescope mount- the part of the telescope on which its optical tube is mounted. Allows you to direct it to the observed area of the sky, ensures the stability of its installation in the working position, and the convenience of performing various types of observations. The mount consists of a base (or column), two mutually perpendicular axes for rotating the telescope tube, a drive and a system for measuring rotation angles.

IN equatorial mount the first axis is directed towards the celestial pole and is called the polar (or hour) axis, and the second lies in the equatorial plane and is called the declination axis; The telescope tube is attached to it. When the telescope is rotated around the 1st axis, its hour angle changes with a constant declination; when turning around the 2nd axis, the declination changes at a constant hour angle. If the telescope is mounted on such a mount, tracking a celestial body moving due to visible daily rotation sky, is carried out by rotating the telescope at a constant speed around one polar axis.

IN altazimuth mount the first axis is vertical, and the second, carrying the pipe, lies in the horizontal plane. The first axis is used to rotate the telescope in azimuth, the second - in height (zenith distance). When observing stars through a telescope mounted on an azimuthal mount, it must be continuously and high degree accurately rotate simultaneously around two axes, and at speeds that vary according to a complex law.

Photos used from www.amazing-space.stsci.edu

Telescope structure

Since ancient times, humanity has been yearning to find out what is there in the sky, beyond the Earth and invisible to the human eye. The greatest scientists of antiquity, such as Leonardo da Vinci, Galileo Galilei, attempted to create a device that would allow one to look into the depths of space and lift the veil of mystery of the Universe. Since then, many discoveries have occurred in the field of astronomy and astrophysics. Every person knows what a telescope is, but not everyone knows how long ago and by whom the first telescope was invented, and how it was designed.

A telescope is a device designed to observe celestial bodies.

In particular, a telescope refers to an optical telescopic system not necessarily used for astronomical purposes.

There are telescopes for all ranges of the electromagnetic spectrum:

b optical telescopes

b radio telescopes

b x-ray telescopes

gamma-ray telescopes

Optical telescopes

According to their optical design, most telescopes are divided into:

b Lens (refractors or diopter) - a lens or lens system is used as a lens.

b Mirror (reflector or catoptric) - a concave mirror is used as a lens.

b Mirror-lens telescopes (catadioptric) - a spherical mirror is used as a lens, and a lens, lens system or meniscus serves to compensate for aberrations.

> Types of telescopes

All optical telescopes are grouped according to the type of light-gathering element into mirror, lens and combined. Each type of telescope has its own advantages and disadvantages, therefore, when choosing optics, you need to take into account the following factors: conditions and purposes of observation, requirements for weight and mobility, price, level of aberration. Let us characterize the most popular types of telescopes.

Refractors (lens telescopes)

Refractors These are the first telescopes invented by man. In such a telescope, a biconvex lens, which acts as an objective, is responsible for collecting light. Its action is based on the main property of convex lenses - the refraction of light rays and their collection at focus. Hence the name - refractors (from the Latin refract - to refract).

It was created in 1609. It used two lenses to collect the maximum amount of starlight. The first lens, which acted as a lens, was convex and served to collect and focus light at a certain distance. The second lens, playing the role of an eyepiece, was concave and was used to transform the converging light beam into a parallel one. Using the Galilean system, it is possible to obtain a direct, non-inverted image, the quality of which is greatly affected by chromatic aberration. The effect of chromatic aberration can be seen as false coloration of details and edges of an object.

The Kepler refractor is a more advanced system that was created in 1611. Here, a convex lens was used as an eyepiece, in which the front focus was combined with the rear focus of the objective lens. As a result, the final image was upside down, which is not important for astronomical research. The main advantage of the new system is the ability to install a measuring grid inside the pipe at the focal point.

This design was also characterized by chromatic aberration, but the effect could be neutralized by increasing the focal length. That is why telescopes of that time had a huge focal length with a tube of the appropriate size, which caused serious difficulties when conducting astronomical research.

At the beginning of the 18th century, it appeared, which is still popular today. The lens of this device is made of two lenses made from different types of glass. One lens is converging, the second is diverging. This structure can significantly reduce chromatic and spherical aberration. And the telescope body remains very compact. Today, apochromatic refractors have been created in which the influence of chromatic aberration is reduced to the possible minimum.

Advantages of refractors:

Simple design, ease of operation, reliability;
Fast thermal stabilization;
Undemanding to professional service;
Ideal for exploring planets, the Moon, double stars;
Excellent color rendering in apochromatic version, good in achromatic version;
System without central shielding from diagonal or secondary mirror. Hence the high contrast of the image;
No air flow in the pipe, protecting the optics from dirt and dust;
One-piece lens design that does not require adjustments by the astronomer.

Disadvantages of refractors:

High price;
Large weight and dimensions;
Small practical aperture diameter;
Limitations in the study of dim and small objects in deep space.

Name of mirror telescopes - reflectors comes from the Latin word reflectio - to reflect. This device is a telescope with a lens, which serves as a concave mirror. Its task is to collect starlight at a single point. By placing the eyepiece at this point, you can see the image.

One of the first reflectors ( Gregory telescope) was invented in 1663. This telescope with a parabolic mirror was completely free from chromatic and spherical aberrations. The light collected by the mirror was reflected from a small oval mirror, which was fixed in front of the main one, in which there was a small hole for the output of the light beam.

Newton was completely disappointed in refracting telescopes, so one of his main developments was a reflecting telescope, created on the basis of a metal primary mirror. It reflected light of different wavelengths equally, and the spherical shape of the mirror made the device more accessible even for self-production.

In 1672, astronomer Laurent Cassegrain proposed a design for a telescope that looked like Gregory's famous reflector. But the improved model had several serious differences, the main one being a convex hyperbolic secondary mirror, which made the telescope more compact and minimized central shielding. However, the traditional Cassegrain reflector turned out to be low-tech for mass production. Mirrors with complex surfaces and uncorrected coma aberration are the main reasons for this unpopularity. However, modifications of this telescope are used today all over the world. For example, the Ritchie-Chretien telescope and a lot of optical instruments based on the system Schmidt-Cassegrain and Maksutov-Cassegrain.

Today, the name “reflector” is commonly understood as a Newtonian telescope. Its main characteristics are a small spherical aberration, the absence of any chromatism, as well as non-isoplanatism - a manifestation of coma close to the axis, which is associated with the inequality of individual annular zones of the aperture. Because of this, the star in a telescope does not look like a circle, but like some kind of projection of a cone. At the same time, its blunt round part is turned from the center to the side, and the sharp part is turned, on the contrary, towards the center. To correct the coma effect, lens correctors are used, which should be fixed in front of the camera or eyepiece.

“Newtons” are often performed on a Dobsonian mount, which is practical and compact in size. This makes the telescope a very portable device, despite the size of the aperture.

Advantages of reflectors:

Affordable price;

Mobility and compactness;
High efficiency when observing dim objects in deep space: nebulae, galaxies, star clusters;

Maximum brightness and clarity of images with minimal distortion.

Chromatic aberration is reduced to zero.

Disadvantages of reflectors:

Stretch of the secondary mirror, central shielding. Hence the low contrast of the image;
Thermal stabilization of a large glass mirror takes a long time;
An open pipe without protection from heat and dust. Hence the low image quality;
Regular collimation and alignment are required and may be lost during use or transport.

Catadioptric telescopes use both mirrors and lenses to correct aberration and construct an image. Two types of such telescopes are in greatest demand today: Schmidt-Cassegrain and Maksutov-Cassegrain.

Instrument design Schmidt-Cassegrain(SHK) consists of spherical primary and secondary mirrors. In this case, spherical aberration is corrected by a full-aperture Schmidt plate, which is installed at the entrance to the pipe. However, some residual aberrations remain here in the form of coma and field curvature. Their correction is possible using lens correctors, which are especially relevant in astrophotography.

The main advantages of devices of this type relate to minimal weight and a short tube while maintaining an impressive aperture diameter and focal length. At the same time, these models are not characterized by stretching of the secondary mirror mounting, and the special design of the pipe prevents the penetration of air and dust inside.

System development Maksutov-Cassegrain(MK) belongs to the Soviet optical engineer D. Maksutov. The design of such a telescope is equipped with spherical mirrors, and a full-aperture lens corrector, the role of which is a convex-concave lens - a meniscus, is responsible for correcting aberrations. That is why such optical equipment is often called a meniscus reflector.

The advantages of MC include the ability to correct almost any aberration by selecting the main parameters. The only exception is higher order spherical aberration. All this makes the scheme popular among manufacturers and astronomy enthusiasts.

Indeed, all other things being equal, the MK system gives better and clearer images than the ShK scheme. However, larger MK telescopes have a longer thermal stabilization period, since a thick meniscus loses temperature much more slowly. In addition, MKs are more sensitive to the rigidity of the corrector mount, so the telescope design is heavier. This is associated with the high popularity of MK systems with small and medium apertures and ShK systems with medium and large apertures.

In addition, Maksutov-Newton and Schmidt-Newton catadioptric systems have been developed, the design of which was created specifically to correct aberrations. They retained Newtonian dimensions, but their weight increased significantly. This is especially true for meniscus correctors.

Advantages

Versatility. Can be used for both ground-based and space-based observations;
Increased level of aberration correction;
Protection from dust and heat flows;
Compact dimensions;
Affordable price.

Flawscatadioptric telescopes:

Long period of thermal stabilization, which is especially important for telescopes with a meniscus corrector;
The complexity of the design, which causes difficulties during installation and self-adjustment.