What is the principle of astronomical telescope? Please attach a picture description!

Basic knowledge of astronomical telescope

Astronomical telescope is the most basic instrument in astronomy at present, and it is also an essential observation tool for astronomical popularization workers and astronomers.

Optical system of astronomical telescope

According to the structure of objective lens, astronomical telescopes can be roughly divided into three categories: refractive astronomical telescopes with lenses as objective lenses; Using a mirror as the objective lens is called a reflective astronomical telescope; A catadioptric telescope consists of a lens and a mirror. Some astronomy enthusiasts often buy a lens, thinking that this will solve the problem of telescope objective. In fact, a lens imaging will produce aberration. At present, the objective lens of normal refraction astronomical telescope is mostly composed of 2 ~ 4 lenses. In contrast, refractive astronomical telescope is widely used and convenient to use, which is more suitable for astronomical popularization.

The optical path of reflective astronomical telescope can be divided into Newton system and Karl seglin system. Generally speaking, for the popularization of astronomy, especially for amateurs with insufficient observation experience, Newton-type reflective telescope is inconvenient to use, its objective lens needs to be coated frequently, and it is also troublesome to maintain. A catadioptric telescope consists of a lens and a mirror. Light from celestial bodies is refracted and reflected. This kind of telescope has the advantages of strong optical power, large field of view and elimination of several main aberrations. This telescope is divided into Schmidt system, Maksutov system and Schmidt-Card-seglin system. According to our many years' practical experience, the 120 refracting telescope produced by Nanjing Astronomical Instrument Factory of China Academy of Sciences is a convenient and practical instrument for astronomy popularization and astronomy enthusiasts.

Optical performance of astronomical telescope

Among the objects of astronomical observation, some celestial bodies have visual planes, and some have no distinguishable visual planes; Some celestial bodies have extremely strong light, while others are extremely weak; Some will glow by themselves, others will reflect light. Observers should choose different astronomical telescopes or adopt different methods to observe according to the observation purpose; Generally speaking, universal astronomical observations are mostly comprehensive, and "one mirror is multi-purpose" should be considered. When choosing an astronomical telescope, we must fully understand its basic optical characteristics.

Aperture of astronomical telescope-refers to the effective diameter of the objective lens, often expressed by D;

Relative aperture-refers to the ratio of the effective aperture of the objective lens to its focal length, also known as the focal ratio, which is often represented by a; That is, a = d/f

Generally speaking, the relative aperture of refractive astronomical telescope is relatively small, usually between115 and 1/20, while the relative aperture of reflective astronomical telescope is relatively large, usually between 1/3.5 and 1/5. When observing a celestial body with a certain viewing surface, the line size of the viewing surface is proportional to F, and its area is proportional to F2. The luminosity of the image is directly proportional to the amount of light collected, that is, it is directly proportional to D2 and inversely proportional to the area of the image, that is, it is inversely proportional to F2.

Magnification-refers to the physical quantity of visual astronomical telescope, that is, the magnification of angle. It is equal to the ratio of the focal length of the objective lens to the focal length of the eyepiece.

When many people mention astronomical telescopes, the first consideration is the magnification. In fact, astronomical telescopes and microscopes are different. The effect of astronomical observation on the ground is influenced by the clarity and tranquility of the earth's atmosphere and the environment of the observation site. Moreover, an astronomical telescope has several eyepieces with different focal lengths, that is, several different magnifications. When observing, the maximum magnification is by no means the best, and the clearest observation target shall prevail.

Resolution angle-refers to the minimum angular distance that an astronomical telescope can resolve. In visual observation, the resolution angle of astronomical telescope is = 140 (angular seconds) /D (millimeters), and d is the effective aperture of the objective lens.

Field of view-refers to the angular diameter of the starry sky seen by astronomical telescope.

Penetration ability-means that on a clear night, the telescope can see the weakest magnitude in the zenith direction. The penetration ability is mainly related to the effective aperture of the telescope.

For example, the optical characteristics of the 120 catadioptric telescope produced by Nanjing Astronomical Instrument Co., Ltd. are: the effective aperture of the main mirror is 120mm, the focal length is 1500mm, the relative aperture is112.5, and the eyepiece magnification is 37.5 times, 60 times, and 60 times. Its viewfinder objective has an effective aperture of 35mm, a focal length of 175mm, a magnification of 7 times and a field of view of 500.

Eyepiece of astronomical telescope

When people understand the basic optical performance of astronomical telescope, they often only pay attention to the objective lens and ignore the eyepiece, which is one of the terminal equipment of the telescope. As a result, no matter how good the telescope is, it can only look up at the sky and sigh.

The eyepiece of astronomical telescope has two main functions: one is to enlarge the image formed by the objective lens, which is very important for observing celestial bodies with observation surfaces and nearby binary stars; Secondly, the outgoing beam is parallel light, which makes the observer comfortable and labor-saving. There are many kinds of eyepieces, among which Huygens eyepiece is commonly used, which is represented by the letter H, and MH or HM represents the improved Huygens eyepiece, which is suitable for low or medium magnification observation. Langsdon eyepiece, denoted by the letter R, is suitable for the eyepiece with crosshair or ruler, and is used for the measurement and observation of low magnification or medium magnification. Chelner eyepiece denoted by the letter K is an improved version of Ransden eyepiece, which eliminates the chromatic aberration of Ransden eyepiece. This eyepiece has a large field of view and is often used for low magnification observation, such as comets or large-area celestial bodies. Steinhale's monocular lens, Chase's undistorted eyepiece, Abbe's undistorted eyepiece and Hick's undistorted eyepiece are all used for high-magnification observation, such as the observation of the details of the planet or the moon surface.

An astronomical telescope should be equipped with a variety of eyepieces to facilitate different observations and maximize its function. Play its due role. I have seen such a situation: a department ordered a better astronomical telescope from abroad, but there were only two eyepieces. However, the manual introduces that it has a variety of eyepieces. Why are there only two? The seller said that it was set when the buyer placed the order. This is a lesson. Therefore, when ordering astronomical telescopes, we must do a good job of research in advance, have complete and reliable information, have experts to check and carefully review the ordering procedures.

Star finder and guide mirror

The main mirror of astronomical telescope is responsible for the main function of observation. However, many astronomical observations can not be successfully completed by the primary mirror alone. It also needs an assistant, and this assistant is a star seeker or a star guide.

In order to quickly search for the celestial bodies to be observed, a small astronomical telescope, namely a star finder, is often attached to the main mirror. Each finder uses a refractive astronomical telescope. Its optical axis is parallel to the optical axis of the main mirror, thus keeping consistent with the goal of the main mirror. Generally, the objective aperture of the viewfinder is about 5 ~ 10 cm, the field of view is about 30 ~ 50, and the magnification is about 7 ~ 20 times. The reticle for calibration is installed on the focal plane. When observing, first use the star finder to find the celestial body to be observed and adjust it to the center of the field of view. At this time, the celestial body is naturally in the center of the field of view of the main mirror.

When the main mirror observes for a long time, in order to correct the tracking error in time, a lookout mirror, called a star guide mirror, is set next to the main mirror. Telescopes used for astronomical popularization also use star finders instead of star guides.

Installation and tracking of astronomical telescope

An ideal astronomical telescope should not only have an excellent optical system, but also solve a series of mechanical problems. For example, how does the lens barrel stand up? In order to observe any celestial body on the horizon, astronomical telescope devices are usually divided into two types according to the choice of axis direction: horizon devices and equatorial devices. In the horizon instrument, the horizon longitude of the celestial body is a mirror image, and when it changes along the horizontal axis, it represents the horizon latitude of the celestial body. Due to the apparent motion of the celestial sphere on Sunday, the two quantities of the celestial body change at any time in the horizon coordinates, indicating only the instantaneous position. Therefore, generally speaking, the horizon is not convenient for long-term continuous observation.

The equatorial device solved this problem. Its axis is parallel to the celestial axis and is called the polar axis. The other axis is perpendicular to the polar axis, which is called declination axis. When the lens barrel rotates around the polar axis, it changes diagonally, and when it rotates around the declination axis, it changes declination. The declination of celestial bodies does not change with the Sunday motion, but is a constant. Therefore, as long as the lens barrel follows the celestial body around the pole, the celestial body can be kept in the field of view. This is the basic principle of tracking celestial bodies. Obviously, this is to overcome the relative position change caused by the earth's rotation. The earth rotates from west to east at a speed of every four minutes 10, and the tracking celestial bodies also move around the polar axis from east to west at a uniform speed of every four minutes 10. How to make the lens barrel rotate like this? The mechanical system that drives the tracking device is called a tachometer. Before this century, the power of the bell was provided by chain hammer or clockwork, and the speed of the bell was controlled by centrifugal governor. At present, the rotating clock is driven by motor, and the speed is controlled by astronomical clock or radio oscillator. Guiding stars is to make up for the tracking error.

It can be seen that in order to popularize astronomy, it is best for astronomical telescopes to be equatorial devices that can track celestial bodies.

Precautions for astronomical telescope

A complete astronomical telescope is a precision optical instrument composed of optics, mechanics and electronics. It should abide by the rules of use: strengthen maintenance; For equatorial devices, the polar axis should be adjusted to the latitude of the observation site and be in the meridian plane; The focusing of astronomical telescope is very important, so we should pay attention to the difference between people and methods; Observing the microclimate caused by the environment can not be ignored; Telescopes should be balanced in all directions.

According to the structure, general astronomical telescopes can be divided into three categories: refractive astronomical telescopes, reflective astronomical telescopes and catadioptric astronomical telescopes.

I. Refractive astronomical telescope

The so-called refractive astronomical telescope is a telescope that has a lens to focus the light of a distant object and display a real image. As an objective lens, it will focus the distant light. The advantage of refractive astronomical telescope is that it is easy to use, and it will not be unclear if it is slightly neglected in maintenance. Because the inside of the lens barrel is sealed by the objective lens and eyepiece, the air will not flow, so it is relatively stable. In addition, the image quality deterioration caused by misalignment of optical axis is better than that caused by reflective telescope. Small-aperture lenses are all spherical, which can be mechanically ground and mass produced.

(1) galileo telescope;

The first astronomical telescope used a concave lens as an eyepiece, and the image seen through the telescope was the same as that seen directly with the eyes. The surface of the earth is convenient, but it can't expand the field of vision. At present, this design is no longer used for astronomical observation.

(2) Kepler telescope:

Using a convex lens as an eyepiece, all refractive telescopes are of this type now, and the imaging is up, down, left and right, but it has no effect on our celestial observation, because the eyepiece is a convex lens, and more than two lenses can be put together to expand the field of vision, which can improve the aberration and eliminate the chromatic aberration.

Second, the reflective astronomical telescope:

Reflective astronomical telescopes use a concave mirror called a primary mirror instead of an objective lens. There is also a small mirror called the secondary mirror, which reflects the light collected by the primary mirror to the outside of the lens barrel, and the light image reflected by the secondary mirror is amplified by the eyepiece. The biggest advantage of reflection type is that because the main mirror is a mirror, the light does not need to pass through the glass, so there is no chromatic aberration at all, and it is unlikely to absorb ultraviolet light or red light, which is very suitable for physical observation such as spectroscopy. Although there is no chromatic aberration, there are other kinds of aberrations. If the reflecting concave surface is ground into a parabolic shape, the spherical aberration can be eliminated. Because the lens barrel can't be sealed, the main mirror is easily affected by smoke and dust, and it is difficult to maintain. At the same time, it is greatly influenced by the air temperature and airflow in the lens barrel, so it is easy to move the positions of the primary mirror and the secondary mirror when carrying, and the optical axis correction is quite complicated and inconvenient to carry. In addition, the diffraction effect of the secondary mirror seat will make the star image of the bright star appear cross-shaped or star-shaped diffraction patterns, which will also reduce the contrast of the image, and the stability of the image is not as good as that of the refractive telescope.

At present, the design of well-known reflective astronomical telescopes can be roughly divided into five types, and we only list two small and medium-sized reflective telescopes on the market.

(1) Newton astronomical telescope;

1668 was invented and designed by Newton, which consists of a parabolic primary mirror and a planar secondary mirror. The plane secondary mirror is installed slightly in front of the focus of the light reflected by the primary mirror, and forms an angle of 45 degrees with the optical axis (as shown in the above figure). This structure is the simplest and the image contrast is high, which is also the choice of most people. Usually the focal ratio is between f4 and f8.

(2) seglin Astronomical Telescope:

Using a hyperboloid as a secondary mirror, the light is focused in front of the main focus, passes through a round hole of the main mirror, and focuses behind the main mirror. Because after a reflection, the lens barrel can be shortened, but the field of view is narrower, the astigmatism is more serious than Newton's, and there is a little field curvature.

Third, the catadioptric telescope:

The advantages of reflection and refraction are basically the same as reflection, but they also have the disadvantages of reflective astronomical telescope. In order to eliminate the comet aberration whose field of view deviates from the optical axis, a lens is used, and the main mirror is a spherical mirror, which is easier to grind than the mirror ... This paper introduces only one kind of catadioptric astronomical telescope which is most widely used.

Schmidt-Descartes telescope

Astrography was invented by Schmidt in 1930. A spherical concave mirror is mainly used as the main mirror to eliminate coma, and an aspheric lens placed in a proper position in front of the main mirror is used as a corrector to correct the spherical aberration of the main mirror. In this way, a wide-angle field of view (up to 40-50 degrees) can be obtained, without spherical aberration and coma, which are common in general mirrors, only slight chromatic aberration produced by the correction mirror. Schmidt telescope for photography can achieve a very small focal ratio (generally between f 1 and f3, and the lowest can reach ÷0.6), so it is very suitable for star field and nebula photography.

Edited on September 7, 2007

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Structure diagram and principle of astronomical telescope

1, the external structure of the astronomical telescope is as follows: 2, the internal structure of the astronomical telescope is as follows: 3, the imaging principle of the astronomical telescope An object passes through the objective lens at a distance of more than twice the focal length, forming an inverted and reduced real image. The real image passes through the eyepiece and becomes an upright magnified virtual image within a focal length of the eyepiece. Because the light entering the light source enters the objective lens, the distance is shortened and the viewing angle is enlarged, so it becomes an enlarged image. That is to say, the small opening angle of distant objects can be enlarged by a certain magnification, which makes them have a larger opening angle in the image space, and can clearly distinguish the objects that were invisible or indistinguishable to the naked eye. Matters needing attention in expanding data 1. Never observe the sun directly through a telescope. Watch the sun through projection or special filtering measures, otherwise it will burn the retina and cause certain damage to the primary mirror. Don't use binoculars as toys. Telescopes are precise optical instruments, so be careful to use and maintain them. Don't think that you can see everything with a telescope. You can really see the details of celestial bodies and celestial bodies through telescopes, but the better the viewing effect, the higher the price. There is no perfect telescope, so it is most important to choose the one that suits you. 4. Every telescope has its proper magnification. Exceeding this multiple will not enhance the resolution, but will make the object very dark and difficult to see. For a telescope with a diameter of 60 mm to 80 mm, the appropriate magnification should be less than 100 times, and almost nothing can be seen when magnified 200 times. 5. If you can't identify more than five constellations in the night sky, don't use a telescope in a hurry, because you can't find observable stars, you can only look at the moon; 6. Astronomical telescopes can usually watch landscapes or animals and plants, and can easily get a higher magnification than binoculars. However, the usage ratio should be below 100 times, and 20-50 times is the most suitable. Baidu encyclopedia-astronomical telescope Baidu encyclopedia-telescope

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Find out the working principle of a high-power optical telescope and attach a picture.

Kepler telescope, a kind of refractive telescope. The objective lens group is also a convex lens, but the eyepiece lens group is a convex lens. The imaging of this telescope is upside down, but the field of view can be designed to be larger. It was first invented by German scientist johannes kepler in 16 1 1 year. In order to form an upright image, some refractive telescopes with this design, especially most binoculars, add an image-turning prism system in the optical path. In addition, almost all refractive telescopes have Kepler optical system.

Kepler principle consists of two convex lenses. Because there is a real image between the two, it is convenient to install the reticle (installed at the focal plane of the eyepiece) and has excellent performance, so at present, military telescopes, small astronomical telescopes and other professional telescopes all adopt this structure. But the imaging of this structure is inverted, so an upright system should be added in the middle.

There are two types of imaging systems: prism imaging system and lens imaging system. Our common typical binoculars with wide front and narrow back adopt a double right-angle prism imaging system. The advantage of this system is that the optical axis is folded twice at the same time, which greatly reduces the volume and weight of the telescope. It is expensive to use a complex set of lenses to invert the image. The Russian 20×50 three-section telescope not only adopts a well-designed lens upright system.

Kepler telescope sees a virtual image, the objective lens is equivalent to a projector, and the eyepiece is equivalent to a magnifying glass.

5 Browse14212017-12-16.

What is the principle of astronomical telescope?

Generally, the imaging is vertical up and down and inverted left and right. Because the eyepiece interface has a 90-degree zenith mirror, so the top and bottom come over, which is usually the case. Some of the more complicated ones are positive, and the cost will be higher. If you say that the simple astronomical telescope has no zenith mirror, it is completely upside down, and it is not a big problem to observe the moon. Of course, the astronomical telescope is enlarged. How can it be reduced? In order to shoot the nebula with a telephoto telescope, a defocusing lens may be used in front of the objective lens to deliberately "reduce" the picture, but that is another matter. The astronomical telescope must be magnified. Who would buy a miniature mirror?

1 Browse65 2018-07-26

How can the astronomical telescope see so far and how to make it!

First of all, the concept of how far a telescope can see is wrong. Our naked eye is an optical instrument. We can see the Andromeda Nebula 2.54 million light years away, but we can't see the nearest extrasolar star proxima centauri (4.2 light years). It doesn't matter how far an optical instrument can see, only how clearly it can see. Production principle: Generally, there are two lens barrels on the astronomical telescope, the large one is the main mirror, which is used to observe the target; The small one is called an image finder, which is used to find the target. It is also called a sight. The eyepiece is an individual and determines the magnification. There will be an f value on the eyepiece, which is the focal length of the eyepiece. Divide the f value of the primary mirror by the f value of the currently used eyepiece, which is the current magnification. Remember, magnification is the standard. The limit magnification of a telescope with a diameter of 6 cm is about 120 times, and the maximum magnification of 8 cm is about 160 times. Astronomical telescope can gather more light and see darker celestial bodies because of the large pupil diameter of aperture ratio's naked eye. Obviously, the farther away an object with the same brightness is, the darker its brightness is, so the telescope can see relatively distant objects. However, it does not mean that all celestial bodies can be seen in this range. For example, M87, which is tens of millions of light years away, looked at it with an astronomical telescope for a whole day, but it doesn't mean that it saw dwarf galaxies and stars closer to him. The larger the well, the higher the resolution of the telescope. However, the number of objects that a telescope can see has nothing to do with the resolution. The resolution of the telescope = wavelength/aperture, so for the same telescope, the resolution of violet light is smaller than that of red light. So how dark the telescope can see has nothing to do with the resolution. References:

Astronomical telescope Baidu encyclopedia

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Working principle of astronomical telescope

The working principle of astronomical telescope is that the objective lens (convex lens) converges the image and magnifies it through the eyepiece (convex lens). Focusing by the objective lens, and then magnifying by the eyepiece, the objective lens and eyepiece are double-separated structures to improve the imaging quality. Increase the light intensity per unit area so that people can find darker celestial bodies and more details. What enters your eyes is almost parallel light, and what you see is a virtual image magnified by the eyepiece. It enlarges the small opening angle of distant objects according to a certain proportion, so that they have a larger opening angle in the image space, so that objects that were invisible or indistinguishable can be clearly distinguished. It is an optical system that makes the incident parallel beams pass through the objective lens and eyepiece and still exit in parallel. Generally, there are three kinds: First, a refractive telescope is a telescope that uses a lens-cutting mirror. There are two kinds: galileo telescope with concave lens as eyepiece; Kepler telescope with convex lens as eyepiece. Because the chromatic aberration and spherical aberration of Dan Toujing objective lens are quite serious, modern refractive telescopes generally use two or more lens groups. 2. Reflective telescope is a telescope with concave reflector and cutting mirror. Can be divided into Newton telescope, seglin telescope and other types. The main advantage of reflective telescope is that there is no chromatic aberration. When the objective lens is a paraboloid, spherical aberration can be eliminated. However, in order to reduce the influence of other aberrations, the available field of view is smaller. The material for making the mirror surface only requires small expansion coefficient, small stress and easy grinding. 3. Refractive-reflective telescope adds a refractive element on the basis of spherical reflector to correct aberration, which can avoid the difficulty of machining large aspheric surface and obtain good imaging quality. There is a famous Schmidt telescope, and a Schmidt correction plate is placed in the center of the spherical mirror. It is an aspheric surface with one side flat and the other side slightly deformed, which makes the central part of the beam slightly converge and the peripheral part slightly diverge, just to correct spherical aberration and coma.

16 Browse 8092019-1-15.