Useful tips on choosing a telescope and accessories
Have you decided to donate a telescope to a friend or child? Great gift! The knowledge of the mysteries of the cosmos, the study of the starry sky have a beneficial effect on the nature of man, on his world perception.
Understanding the beauty and grandeur of the cosmos, we learn to live in harmony with nature. Maybe you want to get yourself a powerful tool and do astrophotography?
The modern market of telescopes, accessible to almost everyone, is quite wide and diverse. You can become the owner of an inexpensive entry-level instrument, or you can purchase a large instrument with the characteristics of professional equipment that astronomers use today. Before exploring the assortment of telescopes that are worthy of your attention, you should decide on the type of optical system of the device, its mount (what it is installed on) and the manufacturer.
There are several optical systems of telescopes most widely used today in the series of amateur equipment: refractors (lens-lens), reflectors (lens-mirror), Cassegrain system,Maksutov-Cassegrain and Schmidt-Cassegrain (systems with a combined set of lenses and mirrors). The choice of the optical system is very important, although you can, of course, choose a telescope that will appeal to you. Here we highlight the main points for optical systems.
Refracting telescopes have a lens in the front of the tube as an objective. They are longer than other systems. The price of a telescope with an increase in the diameter of the lens grows disproportionately, since the manufacture of high-quality large lenses is a complex production process, more complicated than the manufacture of mirrors, for example, for Newton's systems. There is a refractor-apochromat system, which has a shorter pipe length (focus), but a higher price. Such telescopes are often used for astrophotography.
Telescopes of the refractor system are convenient for observations in open areas and are inconvenient for observations from a balcony or from an open window. Although I do not advise you to observe from an open window in principle - the temperature difference in the room and on the street will create turbulent air flows that will strongly distort the image.Watching through the glass of a closed window is basically impossible.
In general, the system of the refractor on the azimuth mount is great for children, because it does not present any particular difficulties with the work. Refractors are not so sensitive to temperature conditions, unlike mirror telescopes.
The optical system of reflectors, for example, the Newtonian system, is fundamentally different from the system of refractors. The lens here is a concave mirror at the rear of the tube. Making mirrors is simpler than lenses, so reflector telescopes with the same lens diameter as the refractor will be much cheaper.
Reflectors are most often installed on an equatorial mount, which can be difficult for children, but at the same time more functional and convenient in long-term observations than azimuth. Such telescopes can be mounted on the Dobson mount - cheap, but not suitable for accurate observations and navigation.
Mirrors have a thin reflective layer and they need to be carefully treated. The most dangerous are regular sudden changes in temperature. After the observations, it is recommended to cover the telescope so that the mirror and other parts of the pipe do not become covered with condensate.Today a wide range of reflectors is available in the assortment from 80–100 mm to 150 and even 250 mm in diameter of the lens.
If the light intensity of the telescope is important to you, if you want to observe weak and distant objects and at the same time save money as much as possible - this type of telescope is for you. Although this does not mean that the system is worse than the others. Here such a rule of division is impossible! Each optical system has its own differences, important advantages and disadvantages.
Telescopes of other optical systems: Maksutov-Cassegrain, Schmidt-Cassegrain
Since the invention of Galileo by the Galileo telescope and its wide distribution, the fact of image distortion (chromatic aberration) has become known, which give lenses, in particular, being an objective in telescope-refractor systems. With this tried one way or another to fight.
Mirror systems are practically devoid of these shortcomings, but others may arise in them - spherical aberration, coma.
To correct the distortions in the mirror systems, optics invented corrective lenses and plates that are installed in the front of the tube. Such systems have a high-quality and clear image, are very compact and transportable.
Surely everyone who was holding a telescope or binoculars in his hands, noticed that there is a desire to lean on something hands, because hand tremor is transmitted to the instrument and the image is trembling, making it difficult to view the details of distant objects and objects. The mechanical moving system and the support on which the telescope is mounted is called a mount.
There are many mount systems, in the amateur telescope range there are three main types: azimuth, equatorial and so-called. Dobson system. Each type of mount has its own advantages and disadvantages.
Azimuthal, for example, is simple and suitable for telescopes of the system refrator, convenient for children.
Equatorial - customizable for the latitude of the place of observation and allowing to direct the telescope at celestial bodies according to the coordinates, it is indispensable for accurate astronomical observations, search for comets, weak sky objects. This system is great for astrophotography - photographing the starry sky, objects.
Dobson's system is simple and uncomplicated, but inconvenient for finding weak objects. Such a system is most often used for large reflectors, which reduces the total cost of the “telescope plus mount” kit, and at the same time you get a powerful telescope.
Frequently asked question: “What is the maximum magnification for this telescope?”
Many for some reason believe that the main parameter of the telescope is an increase, and this is far from the case! Others believe that you can buy an inexpensive telescope, put the magnification 500 times and consider the spiral galaxies. This is also not true! There is a limit for each telescope that is easy to calculate yourself: you need to multiply the aperture (diameter of the telescope lens) in millimeters by 1.4 - this is an increase with a good image quality.
In principle, it is possible to use large magnifications, but here each individual telescope will produce a different resultant image in the eyepiece. There is also an absolute qualitative limit of magnification: the aperture in millimeters is multiplied by 2.
As a rule, a further increase in increases will not give the addition of new details in the picture. The image will increase in size, but at the same time it will "blur" and darken.
That is, more you will show a telescope with a large diameter lens. And eyepieces that form the parameter "magnification", you can additionally buy any.
What a goal - such a telescope!
First telescope. A 70–90 mm refractor, a 110–130 mm Newtonian reflector, or a 90–100 mm Maksutov-Cassegren can be recommended for the role of the first telescope.
Telescope for a child. Children are usually less demanding than adults. Cheap 70-80 mm refractors and reflectors will allow your child to make the first unforgettable walks through the starry sky.
Planetary observations. For serious exploration of the planets, 120–150 mm refractors are best suited. These tools have no central shielding, and therefore they give bright contrasting images.
Observations of deep space objects. The most suitable tools for observing faint galaxies, nebulae and clusters are 200–250 mm reflectors on equatorial or Dobson mounts.
Universal telescope.Tools in this category are designed for people who have not decided which objects they will observe most often. For them, a 100–120 mm refractor, a 130–150 mm reflector, or a 127 mm Maksutov-Cassegren can be the optimal choice.
Transportable telescope. Telescopes built according to the Maksutov-Cassegrain system are light enough and compact for painless transportation to the point of observation.In addition, as a "marching" telescope, you can use a short-focus refractor.
Telescope for astrophotography.For filming celestial objects with long exposures, you will need a stable equatorial mount with a smooth stroke, equipped with electric drives in both axes.
Telescope for ground-based observations.For observation of ground objects, short-focus refractors and Maksutov-Kassegren telescopes, equipped with a wrapped prism (it gives a direct image) and mounted on azimuthal mounts, are most suitable.