Кратко ръководство за рефракторните телескоп: изберете Вашето оборудване разумно

A refractor (also called a refracting telescope) is an optical telescope that uses a system of lenses to collect light and form an image. The refractor, invented in the 17th century, is the earliest type of optical telescope. And nowadays it is still one of the most popular telescope designs in the world, used by both beginning amateurs and professionals.

This simply designed refracting telescope features an objective that consists of a biconvex lens and a biconvex eyepiece. The large biconvex lens collects rays coming from the light source and makes them converge at the focal point or focus where the image is formed. The eyepiece that is placed near the focal point magnifies that image. Unfortunately, refractors suffer from achromatic aberrations due to the inability of a lens to bring all wavelengths of color to the same focal plane. This effect has encouraged scientists to create more complex achromatic and apochromatic telescope designs that have several lenses made of different types of high-quality glass to correct the majority of chromatic aberrations. Apochromatic telescopes are deservedly popular among advanced-level astronomers due to the highest quality of images they produce (although they are quite pricy because of the complexity of the manufacturing process of such lenses).

The refracting telescope, as any other telescope design, has its strong and weak points. There is no one common advice on which telescope you should opt for: you should consider a lot of different factors, such as your level of experience, what objects you are going to observe and where, transportability and weight requirements, level of aberrations, price, and so on. The information provided below will help you make a reasonable purchase decision.

Advantages:

• Have simple design that ensures ease of use and high reliability;
• Do not require much maintenance and collimation;
• Closed optical tube assembly – the interior is protected from dust and air currents that adversely affect image quality;
• Quick thermal stabilization compared to reflectors and catadioptric designs;
• Excellent for observations of the Moon, Solar System planets, double stars (especially large aperture refractors);
• Maximum image contrast due to the absence of effect of the central screening by the secondary or diagonal mirror;
• Good color rendering properties in achromatic and excellent in apochromatic schemes;
• Can be used for terrestrial viewing.

Disadvantages:

• Higher cost per inch of aperture compared to reflectors or catadioptric telescopes;
• As a rule, larger weight and dimensions compared to reflectors and catadioptric telescopes of the same aperture;
• High cost and bulkiness of construction imply limitations on the aperture size;
• Generally less suitable for observations of small and faint deep-sky objects due to practical limitations in the size of the aperture.

Refractor telescopes for beginners

Levenhuk Skyline 50x600 AZ Telescope

An entry-level refracting telescope is probably the best choice for a beginning macrocosm explorer. Refractor telescopes for beginners will introduce observers to the sky by showing the most interesting objects on the celestial sphere, such as the Moon and Solar System planets. As we mentioned in the ‘Advantages’ section, the refracting telescope has a simple design and doesn’t require any special maintenance. You won’t need to collimate the lens, or clean inner surfaces of the tube from dust and dirt, as the tube is closed and sealed (as opposed to reflectors). It is easy to use and very reliable. By choosing a small 70-120mm refractor, you will get a wonderful lightweight and portable tool that can be stored in your house or apartment and used for observations from a balcony, or easily carried to the observing spot in the countryside. All those advantages are also applied to children.

Simplicity of use, light weight; no special maintenance – all these features make refractor telescopes the best instruments for beginners.

TableTop Refractor Telescopes

Levenhuk LabZZ MT2 Table Top Telescope

One more important question you need to solve before buying a telescope is which mount will be the best for your purposes. If you are an ‘always on-the-go’ person, live a very active lifestyle, planning to observe both stars and terrestrial objects, then we recommend that you pay attention to TableTop refractor telescopes.

The main advantages of refractor telescopes installed on simple TableTop tripods are, as expected, high portability and convenience. The whole equipment set fits into a backpack and can be easily transported to the observing site. TableTop mount is also very easy to control; even a kid can manage it without a parent’s help. Of course, you won’t be able to use such a mount with heavy, advanced telescope models. However, if you have (or are planning to purchase) a simple small aperture refractor for entry-level observations, then you can definitely say ‘yes’ to a TableTop mount. It’s also worth mentioning that TableTop mounts can be either alt-azimuth or equatorial. Below you will find information on these two major types of mounts for astronomical telescopes.

Refractor Telescopes with Alt-azimuth Mounts

An alt-azimuth mount is very easy to use - it doesn’t require alignment and therefore any special skills from the observer. This type of mount is very similar to a simple camera tripod. It supports and rotates the optical tube about two perpendicular axes – one vertical (altitude) and the other horizontal (azimuth). Some alt-azimuth mounts are equipped with slow motion controls for more precise and smoother navigation. There are several types of Alt-Azimuth mounts – simple tripods for small refractor and reflector telescopes, Dobsonian mounts for large 200-500 aperture reflectors, and fork mounts for large catadioptric telescopes. These mounts can also be manually or computer controlled (computerized GoTo mounting systems that independently track objects as they move along the celestial sphere). Alt-azimuth mounts are best suited for visual observations of astronomical and terrestrial objects and can also be used for entry-level astrophotography of bright astronomical objects with short exposures.

Refractor telescopes with Alt-azimuth mounts are ideal for beginning macrocosm explorers. Neither refractors nor alt-azimuth mounts require any special preparations before observations. You will be able to start your observations very quickly; you’ll just need to give it a little time to cool down. A small aperture refractor telescope installed on an Alt-azimuth Mount is also a very compact and lightweight instrument that can be easily packed and transported wherever you want to go. It will also be useful in daytime for terrestrial viewing.

Refractor Telescopes with Equatorial Mounts

Levenhuk Skyline 90x900 EQ Telescope

If you already have at least a little experience in astronomy, then you should set your eyes on quality refractor telescopes with equatorial mounts. Equatorial mounts have a more complex design and do require special skills from the user as they have to be aligned each time before observations. The equatorial mount has two axes of rotation - right ascension (RA) and declination (DEC). Once the telescope is aligned with the North Pole, you will only need to move it around one axis (RA) to follow an object’s path in the sky. These mounts are always equipped with slow motion controls and often with motor drives. These features allow for very accurate navigation on even very small celestial objects and provide advanced capabilities for astrophotography. These mounts are also universal – convenient for use with any telescope type. Although, in general, equatorial mounts are more bulky compared to simple Alt-azimuth ones, Eq1 and Eq2 models are still quite compact and can be transported to the observing sites without any problems. Refractor telescopes, especially apochromatic ones, installed on quality Equatorial Mounts are ideal tools for astrophotography of planets and the Moon – and we are about to cover that in the below section.

Refractor Telescopes for Astrophotography

Bresser Messier NT-203/1000 Hexafoc OTA

Astrophotography is a truly fascinating hobby! If you want to try your hand at this new pursuit, there are three main things to consider: type of telescope, mounting system, and, of course, the camera that you are going to use.

A good mount is, perhaps, the most important parts of the whole astrophotography equipment setup. To do quality shots you will need a solid motor­driven tracking mount. We recommend using quality German equatorial mounts – they allow for precise and very accurate tracking of objects as they move along the skies. That means you will be able to make high quality, long exposure images.

Achromatic refractor telescopes are great for beginner level planetary and lunar astrophotography. If you want to do serious astrophotography, you need to consider buying a quality apochromatic refractor telescope installed on German equatorial mount. Achromatic aberrations become more noticeable when you do astro imaging than simple visual observations. Apochromatic telescopes reduce those aberrations to a minimum, providing exceptionally sharp and clear astro shots.

And the last but not least part of the astrophotography equipment set is, of course, a camera! You can start by using your own DSLR camera and if you are not happy with the results, switch to a special CDD camera that will give you more potential for astro imaging.

Summary

Entry-level refracting telescopes are ideal for children and all beginning explorers of the skies. They are lightweight, compact, easy to use and maintain, and don’t require any collimation requiring special skills and knowledge. High-end apochromatic refractors are great for professional observers as they provide quality views with no effect of chromatic aberration. That makes them ideal instruments for both visual observations and astrophotography.

Choosing optical equipment is not an easy task – if you have any hesitation on what telescope type will be the best for your needs, feel free to contact our Support Team, who will help you make the right decision.

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