The telescope is used for How to choose the right modern telescope. Pros and cons of optical circuits

26.10.2017 05:25 2877

What is a telescope and why is it needed?

A telescope is an instrument that allows you to view space objects at close range. Tele is translated from the ancient Greek language - far away, and scopeo - I look. Outwardly, many telescopes are very similar to a spyglass, so they have the same purpose - to zoom in on images of objects. Because of this, they are also called optical telescopes because they zoom in on images using lenses, optical materials similar to glass.

The birthplace of the telescope is Holland. In 1608, spectacle makers in this country invented the spotting scope, the prototype of the modern telescope.

However, the first drawings of telescopes were found in the documents of the Italian artist and inventor Leonardo da Vinci. They were dated 1509.

Modern telescopes for greater convenience and stability are placed on a special stand. Their main parts are the lens and the eyepiece.

The lens is located in the part of the telescope farthest from the person. It contains lenses or concave mirrors, so optical telescopes are divided into lens and mirror telescopes.

The eyepiece is located in the part of the device closest to the person and is turned to the eye. It also consists of lenses that magnify the image of objects formed by the lens. In some modern telescopes used by astronomers, instead of an eyepiece, a display is installed showing images of space objects.

Professional telescopes differ from amateur ones in that they have a high magnification. With their help, astronomers were able to make many discoveries. Scientists conduct observations in observatories of other planets, comets, asteroids and black holes.

Thanks to telescopes, they were able to study in more detail the Earth's satellite - the Moon, which is located at a relatively small distance from our planet by space standards - 384,403 km. The magnifications of this instrument make it possible to clearly see the craters on the lunar surface.

Amateur telescopes are sold in stores. According to their characteristics, they are inferior to those used by scientists. But with their help, you can also see the craters of the moon,

optical telescope designed to observe distant objects in the night sky. The main characteristics of telescopes: objective diameter and magnification. The larger the diameter of the lens, the more light it will collect, and the weaker objects will become visible through it. The magnification determines how small details can be seen on the surface of the planets, the Sun, the Moon. Due to the wave properties of light, the resolving power of a telescope, and hence the maximum possible magnification, is determined by the diameter of its lens. The larger the lens, the more magnification it can give. With an increase numerically equal to the diameter of the lens in millimeters, the maximum resolution is achieved, therefore such an increase is called resolving. A further increase in magnification does not add new details, but only degrades the image quality. As the diameter of the lens increases, the amount of light collected by it also increases, however, excess light, scattering on optical surfaces, forms numerous flares and halos that spoil the image and prevent close objects from being seen. Therefore, as the diameter of the telescope objective increases, so do the requirements for the quality of optics.

All existing telescopes by design can be divided into two large groups: mirror (reflectors) and lens (refractors).
The most common are mirror telescopes built according to the Newtonian optical scheme, which have a simple design and low cost. They are a tube open at one end, at the other end of which there is a concave mirror that serves as an objective. The tube itself plays the role of a hood, passing parallel beams of light coming from the object of observation, and its inner walls have a black matte surface, absorbing the rest of the light. A parallel beam of rays falls on the main mirror and, reflected from it, is refracted in the diagonal mirror at an angle of 90 degrees and is projected into the focal plane of the eyepiece. The magnification of the telescope can be changed due to the presence of a set of interchangeable eyepieces.

Mirror telescopes have a number of disadvantages:
1. With an increase in the diameter of the mirror, the length of their tube rapidly increases, which makes them difficult to transport.
2. Distortions introduced by a diagonal mirror and braces fixing it spoil the image and degrade the resolution of the telescope, as well as shield part of the light flux.
3. The field of view is severely limited by the length of the pipe.
4. Dust gets into the open part of the pipe, as well as air flows that make it difficult to observe at high magnifications.
5. When cleaning the mirror, it is necessary to remove it, thereby violating its alignment, and the telescope has to be periodically adjusted.

Lens telescopes (refractors) are more expensive, but they have a number of advantages over mirror ones. They are a closed tube with an objective lens at the inlet, which does not get dust and foreign particles, there is no air flow, there is no central shielding, which significantly increases the resolution, and they have low light scattering. Refractors do not need constant alignment, but they also have a significant length.

All telescopes come with a tripod that allows you to install the device in any convenient place. For the convenience of pointing telescopes at the object of interest, they usually have an optical viewfinder. In the simplest case, these are two frames fixed on the body so that the axis passing through the centers of their holes is parallel to the optical axis of the telescope. Sometimes the viewfinder is a high-aperture spotting scope with a magnification of up to 8x. The most sophisticated telescope models have an automatic drive that allows you to track objects as they move across the night sky. To observe the Sun, it is necessary to use special light filters included with the telescope.

Material provided by Yukon
www.yukonopticsglobal.com
Compiled by: Babich A.E., Abakumov A.V.
Consultant: Buglak N.A.

Several turbulent centuries have passed since the time of Galileo, in which scientific and technological progress has never stood still. Astronomy has ceased to be just a science, because a huge segment of lovers of stargazing has formed. And to the question why do you need telescope they answer with their heart, with a genuine thirst to touch the mystery and mystery, with a sincere desire to embrace infinity with their eyes. Who are they? Mom and dad, picking up a school atlas of the starry sky, for the first time explain to their son what space, nebulae, the Milky Way are. Or just a novice astronomer who dreamed of seeing the rings of Saturn since childhood and finally realized his cherished dream.

Just then, armed with optics, go beyond the usual boundaries of the visible world with your eyes. In order to be convinced firsthand, not from the Internet or textbooks, how the sky is dotted with a diamond scattering of stars. It is unlikely that a person will ever be able to contemplate absolutely all the delights of the Universe, but what can be available for study right now is truly impressive.

Scientific entertainment. The telescope can become a visual teaching tool if parents want their child to develop intensively and expand their horizons. At the same time, the learning process itself can have a playful form - astro travel will be of interest to almost everyone, regardless of age, even preschoolers.

Astrophotography is a special kind of magical art that has captivated hundreds of thousands of followers! Those who have started doing this seriously get amazingly beautiful pictures. Currently, many Internet resources have been created where they can be boasted and discussed. In order to master this simple matter, you can purchase a digital camera for a telescope. It connects very easily, the image can be displayed on a computer in real time. Another way is to attach an existing SLR camera using a special t-ring.

And why do professionals need telescopes - employees of observatories, researchers, professors and academicians? So that we can one day correctly use the new knowledge. Mankind has already been able to overcome the force of gravity and I want to believe that the era is near in which we will be able to send spaceships to the most distant galaxies. And we would also like to live in peace in safety - to be sure that a meteorite or comet detected in time will not harm our home - the Earth.

> Types of telescopes

All optical telescopes are grouped according to the type of light-collecting element into mirror, lens and combined. Each type of telescope has its advantages and disadvantages, therefore, when choosing optics, the following factors should be taken into account: the conditions and objectives of observation, requirements for weight and mobility, price, and the level of aberration. Let's 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 is responsible for collecting light, which acts as an objective. Its action is based on the main property of convex lenses - the refraction of light rays and their collection in focus. Hence the name - refractors (from the Latin refract - to refract).

It was created in 1609. It used two lenses, with the help of which the maximum amount of starlight was collected. The first lens, which acted as a lens, was convex and served to collect and focus light at a certain distance. The second lens, which played the role of an eyepiece, was concave and was used to turn the descending light beam into a parallel one. With Galileo's system, you can get a straight, upside-down image, the quality of which suffers greatly from chromatic aberration. The effect of chromatic aberration can be seen as a false painting of the details and edges of the 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 back focus of the objective lens. From this, the final image was inverted, which is not essential 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 scheme was also characterized by chromatic aberration, however, the effect of it could be leveled by increasing the focal length. That is why the telescopes of that time had a huge focal length with a tube of the appropriate size, which caused serious difficulties in 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 of different types of glass. One lens is converging, the other is diverging. This structure can greatly reduce chromatic and spherical aberrations. And the body of the telescope remains very compact. Today, apochromatic refractors have been created in which the influence of chromatic aberration is reduced to a possible minimum.

Advantages of refractors:

Simple structure, easy operation, reliable;
Fast thermal stabilization;
Undemanding to professional service;
Ideal for exploring planets, moon, double stars;
Excellent color reproduction in apochromatic performance, good - in achromatic;
System without central shielding from a diagonal or secondary mirror. Hence the high contrast of the image;
Lack of air flow in the pipe, protection of optics from dirt and dust;
One-piece lens construction requiring no adjustments by the astronomer.

Disadvantages of refractors:

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

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

One of the first reflectors ( Gregory's telescope) was coined 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 based on a metal main mirror. It equally reflected light with different wavelengths, and the spherical shape of the mirror made the device more accessible even for self-production.

In 1672, astronomer Lauren Cassegrain proposed a scheme for a telescope that outwardly resembled the famous Gregory reflector. But the improved model had several serious differences, the main of which was a convex hyperbolic secondary mirror, which made it possible to make the telescope more compact and minimized the 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 around the world. For example, the Ritchey-Chrétien telescope and the mass 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 near the axis, which is associated with the unevenness of individual annular aperture zones. Because of this, the star in the telescope does not look like a circle, but like a projection of a cone. At the same time, its blunt rounded part is turned from the center to the side, and the sharp one, on the contrary, to 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 Dobson 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;

The brightest and sharpest images with minimal distortion.

Chromatic aberration is reduced to zero.

Disadvantages of reflectors:

Stretch secondary mirror, central shielding. Hence the low contrast of the image;
Thermal stabilization of a large glass mirror takes a long time;
Open pipe without protection from heat and dust. Hence the poor image quality;
Requires regular collimation and alignment, which may be lost during use or transport.

Catadioptric telescopes use both mirrors and lenses to correct aberration and build images. Two types of such telescopes are in great 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 pipe inlet. However, some residual aberrations in the form of coma and field curvature remain here. Their correction is possible by using lens correctors, which are especially relevant in astrophotography.

The main advantages of devices of this type relate to the minimum weight and short tube while maintaining an impressive aperture diameter and focal length. At the same time, these models are not characterized by extensions of the attachment of the secondary mirror, and the special design of the pipe excludes the penetration of air and dust into the interior.

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, which is a convex-concave lens - the meniscus, is responsible for the correction of 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, ceteris paribus, the MC system gives better and clearer images than the SC scheme. However, larger MK telescopes have a longer thermal stabilization period, since the thick meniscus loses temperature much more slowly. In addition, MCs are more sensitive to the stiffness of the corrector mounting, so the telescope design is heavy. This is the reason for the high popularity of MC systems with small and medium apertures and SC systems with medium and large apertures.