How do astronomical telescopes see things? (Help me! )

Definition of scientific terms of astronomical telescope

English name: astronomical telescope English name: astronomical telescope definition: an astronomical observation device that collects celestial radiation and can determine the direction of the radiation source, usually referring to an astronomical optical telescope with focusing and imaging functions. Discipline: astronomy (first-class discipline); Astronomical Instruments (two disciplines) This content is approved and published by the National Committee for the Examination and Approval of Scientific and Technical Terminology.

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Hubble telescope astronomical telescope is an important means to observe celestial bodies. It is no exaggeration to say that there would be no modern astronomy without the birth and development of telescopes. With the improvement of telescope performance in all aspects, astronomy is also experiencing a huge leap, which rapidly promotes human understanding of the universe.

Representation method of telescope

Basic representation of telescope

There are only some slight differences in the aperture (diameter, mm) of magnitude X objective lens and the specifications of different types of telescopes, but they are not out of this mode. The following are explained one by one: the representation method of fixed magnification telescope (also the most common telescope): magnification x objective aperture (diameter, mm), for example, 7×35 means that the magnification of this telescope is 7 times and the objective aperture is 35mm；; 10×50 means that the magnification of this telescope is 10, and the aperture of the objective lens is 50 mm ... Tube Wave Ed Astronomical Telescope.

Representation method of specifications of continuous zoom telescope: The continuous zoom telescope is represented by "minimum magnification-maximum magnification x objective aperture (diameter mm)", for example, 8-25x25 means that the minimum magnification of this telescope is 8 times and the maximum magnification is 25 times, which can be changed continuously between 8 times and 25 times, and the aperture is 25mm. The expression of fixed zoom telescope: low magnification/high magnification (/higher magnification) x objective aperture (diameter mm), and sometimes the expression of minimum magnification-maximum magnification x objective aperture (diameter mm) is used. For example, 15/30*80 refers to a telescope with a magnification of 15, a fixed zoom of 30 times, and an aperture of 80 mm The representative of a waterproof telescope: WP (waterproof) is generally added to the back of the telescope model, for example, a waterproof telescope with a magnification of 8X30WP and an objective aperture of 30 mm. Representation method of wide-angle telescope: generally, WA (wide angle) is added at the back of the telescope model. For example, 7X35WA refers to a wide-angle telescope with a magnification of 7 times and an objective lens diameter of 35mm. It is immoral for some dealers to take the product of the multiplication of the front and back numbers as the magnification of the telescope to deceive consumers, and some dealers even arbitrarily expand the two numbers to deceive consumers. I once saw a DCF telescope with the size of 10x25, but it was actually marked with 990x99990. What is the concept of a 990-fold telescope with a diameter of 99990mm?

What is the magnification of the telescope?

Telescope magnification: The magnification of a telescope refers to its ability to magnify objects. For example, if you observe an object with a 7-fold telescope, the effect of observing an object at a distance of 700 meters is similar to that of observing it with the naked eye at a distance of 100 meters (of course, the effect is worse due to the influence of the environment). Many people always think that the higher the magnification, the better. Some dealers and manufacturers also attract and deceive consumers with false high magnification. Some telescopes on the market are actually marked 990 times! In fact, the reasonable magnification of the telescope is related to the diameter and observation mode of the telescope: the larger the diameter, the higher the magnification, and the one with the bracket can be higher than the one with the hand. The greater the magnification, the worse the stability, the smaller and darker the observation field of view, the greater the jitter, and the greater the influence of respiratory airflow and air fluctuation. 7- 10 times is most suitable for hand-held binoculars, and it is best not to exceed 12 times. If the magnification of the telescope exceeds 12 times, it will be inconvenient to observe by hand. Most military telescopes in the world are 6- 10 times. For example, domestic military telescopes are mainly 7 times and 8 times, because clear and stable imaging is very important.

What is the field of view of the telescope?

Field of view refers to the size of the range observed within a certain distance. The larger the field of vision, the wider the observation range and the more comfortable it is. The visual field is generally expressed by the visual field (observable width) and visual angle at a kilometer. There are three common representations: one is to use the angle directly, such as the angle of view: 9; The second is the visual range of kilometers, such as the visual field:158m/1000m; The third type is a thousand-yard ruler, which is actually similar to the second type. For example, the visual field vies is 288 ft/1000 y. Generally speaking, the larger the aperture, the lower the magnification and the larger the visual field, but the design of the eyepiece group is also very important.

What is the diameter of the exit pupil?

The exit pupil diameter is the spot size formed on the eyepiece after the image passes through the telescope. The exit pupil diameter can be obtained by the following formula: objective lens/magnification = exit pupil diameter. It can be seen that the larger the objective lens, the lower the multiple and the larger the exit pupil diameter. Theoretically, the larger the diameter of the exit pupil, the brighter the observed scene, which is beneficial to observation in dim light. Therefore, when choosing a telescope, we should try to choose a telescope with a larger pupil diameter, so is the bigger the better? Not really, because when we use the telescope normally, it is mostly during the day. At this time, the pupil of the human eye is very small, only about 2-3 mm. At this time, if the diameter of the exit pupil is larger than 4 mm, most useful light will not be absorbed by the human eye, but will be wasted. The pupil of the human eye can only reach about 7 mm at dusk or in the dark. So generally speaking, it is enough to choose the exit pupil diameter not less than 3 mm, so the exit pupil diameter is also called dusk factor.

What is a coating? What is the function of coating?

If you pay attention to observation, you will find that there are different colors outside the objective lens of the telescope, such as red, blue, green, yellow, purple and so on. This is commonly called coating. What is the function of lens coating? The purpose of lens coating is to prevent fog white caused by light reflecting diffused light on the lens, support reflection, increase light transmittance, increase color contrast and vividness, and improve observation effect. Generally, the more, deeper and thicker the coating, the better the viewing effect and the higher the brightness. The color of the coating depends on the optical materials and design requirements. The thinner the coating, the smaller the reflection, the better. Commonly used are blue film and red film. Blue film is a traditional coating, and red film appeared in the first half of last century. Many people think that red movies are better than blue movies. There are many bright red thin-film telescopes on the market now. Some dealers call this kind of coating "infrared", "sub-infrared", "ruby coating" and so on. Finally, they will tell you that this is an all-weather infrared night vision telescope, which can observe at night. Please don't be fooled by mirror friends. The real infrared night vision device is photoelectric cell imaging, which is completely different from telescope in structure and principle. It can't be used during the day, and it needs electric observation. In fact, when light penetrates the glass, it will inevitably cause some reflection and reduce the brightness. After the red film is coated, the brightness will be reduced even more because of the serious reflection. This kind of telescope is usually used to reduce the brightness when the sun is strong in the snow. In general, blue film is excellent (many famous cameras and camera lenses are coated with blue film, which is why).

What do DCF, UCF and PCF mean?

DCF, UCF and PCF are the customary names for telescope models. DCF refers to a straight telescope with behan prism, UCF refers to a small telescope with Paul prism, which is often said to be little Paul, with inverted prism structure, and PCF refers to a large telescope with Paul prism, which is often said to be a big Paul portable astronomical telescope.

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Edit the operation of this astronomical telescope.

Generally, an astronomical telescope has two lens barrels. The big 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. Every time we take the telescope out of the box and install it or move it greatly, we have to readjust the optical axes of the two mirrors to create a convenient observation environment. First of all, a simple operation method: the structure of astronomical telescope.

structure

1, the main mirror consists of objective lens (front lens group), focusing system and eyepiece (rear lens group). The lens barrel will be marked with the focal length of the main mirror, which is indicated by F, F600 means that the focal length of the main mirror is 600 mm, and the main mirror is marked with the aperture, and 80 mm means that the aperture is 80 mm. Please note that the aperture is the first criterion to determine the performance of the telescope, and the larger the aperture, the better. 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. If it exceeds this range, the object cannot be seen clearly. In addition, the field of vision of astronomical telescope will not be as wide as that of binoculars. If you want to see a wider area, you can choose an eyepiece with a large f value (such as 20mm, 25mm, 40mm), otherwise the viewing range will be reduced (such as 8mm, 12mm, 4mm). The eyepiece field of view of a general household astronomical telescope is 1 degree (two full moons in diameter, which means that your field of view can hold two full moons). Focusing system is a device to adjust the definition. The star finder is a very important accessory, especially for beginners, because its function is to find the target. So why did he find the target? This is relative. As we said above, the field of view of a telescope is 1 degree, while the field of view of a star finder can reach 6- 10 degree, so a star finder with a large field of view is easier to find the target than the main mirror. From the eyepiece of the viewfinder, we can see that there is a crosshair in the field of vision. This is the positioning device, and how to use it will be discussed below. Another device of the viewfinder is that it has three screws to adjust the direction of the viewfinder, which will be mentioned below.

operating procedure

1. Adjust the optical axis of the main mirror and viewfinder to be parallel. After installing the telescope, we first choose a relatively large building target, such as chimney, outdoor unit of air conditioner, etc. Don't worry about the star seeker. First, choose the eyepiece with the largest F value for the telescope and install it on the main mirror (generally 20mm or 8mm), and use the main mirror to slowly find the object you want to see. Take a sign on the outdoor unit of an air conditioner as an example. We choose large objects to make the main mirror easy to find. Large objects are easy to find, so we adjust the focal length system to make the scene clear and make the image in the center of the main mirror. Once found, lock all tripods. Pay attention, carefully observe the influence in the primary mirror, draw a cross average of the primary mirror's field of vision in your mind, and see which part of the image the central point is. 2. Adjust the main mirror of the viewfinder. The image has been set. Let's adjust the viewfinder. Turn the three screws on the viewfinder and adjust slowly. Adjust the image of the main mirror center to the center of the viewfinder crosshair as much as possible. Be patient. This may be the most anxious time. It should be noted here that sometimes we do adjust the influence to the center, but observing the three screws, it is possible that one of them does not butt against the viewfinder, which means that the adjustment is unsuccessful and only accidental, so we must observe that the three screws butt against the lens barrel, even if they only touch a little, because moving the mirror will not affect the viewfinder in the future. When the image is adjusted to the center, the adjustment of the optical axis is completed. 3. The purpose of the above two links is to make the optical axes of the two lens barrels parallel, instead of observing an object. Must understand. Well, when the optical axes of the two mirrors are parallel, we can observe all the objects. The specific operation is as follows: loosen the newly locked tripod and slowly move in the general direction of the observed object, gently, otherwise the star finder may shake, and the previous work will be in vain. After moving to the approximate position, first observe and aim through the viewfinder, and put the observed object in the middle of the viewfinder cross (turn the tripod, not the viewfinder). After reaching the center, observe the main mirror, and you will find that the observed object honestly appears in the field of vision of the main mirror, and it becomes clear to adjust the focal length. This is because the optical axes are parallel. If you can't see it, it still means that the optical axis is not adjusted well, or you accidentally moved the viewfinder when moving, so you can only adjust it patiently.

Edit the basics of this paragraph.

Optical type

1, refractive type: easy to use, large field of vision, bright star image, but chromatic aberration, which will reduce the resolution, and easy to use and maintain. 2. Reflective type: there is no chromatic aberration, but coma and astigmatism are large, which makes the edge image of the visual field worse; Newton mirror is commonly used, and its optical system is simple. At the same price, the available mirror has the largest aperture and the strongest light collection ability. 3. Refraction: It combines the advantages of refractor and reflector: large field of view, good imaging quality, short lens barrel and easy to carry. There are two types: Schmidt-Ka seglin and Maksutov-Ka seglin.

Basic optical performance parameters

1, aperture: The effective aperture of the objective lens theoretically determines the performance of the telescope. The larger the aperture, the stronger the light gathering ability, the higher the resolution and the larger the available magnification. 2. Concentrating power: Concentrating power, the ratio of the light received by the telescope to the light received by the naked eye. The diameter of a person's pupil is about 7mm when it is fully opened. 70mm diameter telescope, the light collection capacity is 70/7= 100 times. 3. Resolution: The ability of the telescope to distinguish image details. Resolution is mainly related to aperture; 4. Magnification: the ratio of the focal length of the objective lens to the focal length of the eyepiece. For example, Pioneer 60/700 astronomical telescope uses H 10mm eyepiece, and the magnification = objective 700mm/ eyepiece 10mm = 70 times; The larger the magnification, the larger the image you see. The larger the magnification, the better. Generally, the maximum available magnification is not more than 1.5 times the aperture mm. When the maximum effective magnification is exceeded, the image will become larger, but the definition will not be improved. 5. Focal length ratio: the ratio of the focal length of the objective lens to the aperture, which is equivalent to the aperture on the camera lens. If the aperture is constant, the longer the focal length of the objective lens is, the greater the focal ratio is, and it is easy to obtain higher magnification; The shorter the focal length of the objective lens, the smaller the focal ratio, and it is not easy to get a higher magnification, but the image is brighter and the field of view is larger. * short focal length mirror (small focal ratio, focal ratio 15): suitable for observing the moon and planets; * medium focal length mirror (medium focal length ratio, 6

Support mechanism

1, horizon type: simple structure and use, low adjustment accuracy, unable to track celestial bodies, suitable for beginners; 2. Equatorial instrument: The equatorial instrument is used to offset the rotation of the earth and track the movement of celestial bodies during observation; Complex structure and use, high adjustment accuracy; There are manual and electric magnetic declination meters. Manual declination tracker is suitable for special astronomical observation, and high-grade electric declination tracker is mostly used for special astronomical tracking photography and observation research. Beginners can choose manual declination instrument after they are familiar with horizontal support; The first adjustment may be complicated, but it will be much easier to observe the starry sky after familiarity; When amateurs study astrophotography, they often use electric tracking equatorial instrument (conductance), but the price is more expensive.

Optical quality discrimination

During the day, you can use a telescope to observe distant buildings and move the outline of the buildings to 1/4 of the field of vision. If the orange or blue-purple on the outline is particularly obvious, or the outline is particularly curved, the optical quality will be poor. Look at the leaves in the distance Generally, a telescope with a diameter of 60mm can see the Ye Jin of leaves 40 meters away, indicating that the optical quality is very poor (60/700 tube wave pioneers can see the leaves of phoenix trees 60 meters away); When observing stars at night, if you see stars with obvious colors, or the stars at the edge of the field of vision are dragging their tails, the length of the tails is twice that of the stars, indicating that the optical quality is very poor and not suitable for astronomical observation; * Choose 3 1.7mm( 1.25 inch) large eyepiece interface to obtain better optical quality.

Precautions for use

1, you must never watch the sun directly through a telescope, and you must watch the sun through projection or special filtering measures; 2, don't use the telescope as a toy, the telescope is a precision optical instrument, so be careful to use and maintain it; Don't think that you can see everything with a telescope. You can really see celestial bodies and details on 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 ~ 80, the appropriate magnification should be less than 100, 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.