How To Choose a Telescope: A Complete Telescope Buying Guide
This is a complete Telescope Buying Guide, Which will help you to choose a right telescope for your need.
When buying a telescope for the first time, a person is usually confused by the problem of choosing the right model from the whole variety of tools available on sale.
First of all, it is necessary to realize that the ideal tool that is equally well suited for all types of astronomical observations and at the same time affordable, price, size, weight and other parameters, simply does not exist.
Therefore, the choice of any telescope is always a compromise. But if you determine in advance what the main purpose of the instrument is, the problem of choosing a telescope will be greatly simplified!
So, if the telescope will be used mainly for observations of the starry sky, then it will not be required to give a direct image of objects and focus on close objects (ground-based).
With the exception of planets, the moon, the sun and nearby star clusters, astronomical objects are rather dim.
However, for beginner amateur astronomers, the Moon and planets are of most interest, therefore, for their observations, the capabilities of a telescope with a small diameter of the lens (main mirror or lens) will be quite sufficient.
Over time, many astronomy enthusiasts have a desire to move on to the study of distant galaxies, nebulae, star clusters (open and globular) and other objects of distant Cosmos (deep-sky).
This leads to the need to purchase a telescope with a larger aperture (lens diameter), which will allow you to see even weaker objects in the starry sky.
It should not be forgotten that at the same time as the diameter of the lens increases, so does the cost of the telescope, its dimensions and weight category.
Perhaps the most popular among amateur astronomers are the Newton system reflectors, the lowest cost per centimeter of aperture.
Due to this, reflectors of medium and large diameters (150 mm – 250 mm) are widely used, which are excellent for observing faint objects of the far Cosmos, faint clusters, galaxies, nebulae, comets, etc.
When observing the Moon and planets, a clear, very contrasting image is required which provide telescopes-refractors.
They practically do not require maintenance and care, which makes them very convenient to use, but they significantly lose in price to reflectors with the same aperture.
For beginners, a short-focus refractor with a diameter of 70 mm – 120 mm is suitable.
The compact size and large field of view make such tools indispensable for exploratory walks in the starry sky, but at the same time they are suitable for serious observations and even professional studies of the sky!
Mirror-lens telescopes of the Maksutov-Cassegrain and Schmidt-Cassegrain systems are a good compromise for an astronomy lover who wants to have a universal mobile instrument suitable for various types of astronomical observations.
The compact design makes such telescopes very transportable even with sufficiently large apertures, although their price is usually higher than the price of reflectors and refractors.
For ground-based observations, refractors or mirror-lens telescopes will be most suitable, since the reflectors on the reflectors are located on the side of the pipe and will have to be observed sideways to the object of observation.
With such observations, telescopes with a moderate focal length (400 mm – 800 mm) are most preferable, since it is easier to get a large field of view with them, which gives considerable comfort to the observations.
Speaking about ground-based observations, one should not forget what image the telescopes of different models and types give.
For example, in the reflectors of the Newton system, the image is always built upside down.
In refractors and mirror-lens telescopes of Maksutov-Cassegrain and Schmidt-Cassegrain, for the convenience of observing objects, an additional optical element is usually placed in front of the eyepiece, a diagonal mirror. It breaks the optical axis by 90 degrees, and the image becomes not inverted, but mirrored.
To obtain the correct (not inverted and not mirror) image in telescopes, refractors and telescopes of the Maksutov-Cassegrain and Schmidt-Cassegrain systems, a special prism is installed instead of the diagonal mirror. Newton’s reflectors are not used to obtain a direct image in principle.
If an astronomy lover plans to store a telescope in a city apartment, taking it out for observation on the street or going out of town with it, then its size and weight can become an important factor in choosing an instrument. In this case, you need to pay attention to compact mirror-lens telescopes or short-focus refractors.
After you have decided what observational goals you are going to set for your telescope, the following question will arise: Which telescope can best meet your observation requirements?
Consider the possible goals that the telescope must meet:
The first telescope, the role of the first telescope can be recommended 70 mm – 90 mm refractor, 110mm – 130 mm Newton reflector or 90mm – 100 mm Maksutov-Cassegrain.
Telescope Buying Guide: To the point!
Telescope for a child: Usually children are less demanding on the instrument than adults. Inexpensive 70 mm – 90 mm refractors and reflectors will allow the child to make the first unforgettable walks in the starry sky and distant earth objects.
Planetary observations: 120 mm – 150 mm refractors are best suited for serious planetary exploration. Such telescopes lack central shielding and give bright contrasting images of objects.
Observations of deep space objects (deep-sky): The most suitable instruments for observing distant galaxies, nebulae and clusters are 200 mm – 250 mm reflectors on equatorial mounts or Dobson mounts.
Universal telescope: tools from this category are intended for people who have not finally decided which objects they will observe most often (ground or space objects). For them, the best choice may be 100 mm – 120 mm refractor, 130 mm – 150 mm reflector or 90 mm – 120 mm Maksutov-Kasegren.
Transportable telescope: Telescopes constructed according to the Maksutov-Cassegrain system are usually made quite light and compact, suitable for painless transportation to the observation site. In addition, a short-focus refractor telescope can be used as a field tool.
Astrophotography telescope: for shooting celestial objects with long exposures, a stable equatorial mount will be required, equipped with electric drives on both axes (or, at least, along the right ascension axis).
Telescope for ground-based observations: Short-focus refractors and Maksutov-Cassegrain telescopes equipped with a wraparound prism that gives a direct image and mounted on azimuth mounts or photo tripods are most suitable for observing ground-based objects.
Good luck in choosing a telescope and unforgettable observations of the starry sky!
Related Article: Best Telescope For Teenager
For your interest, we have defined 3 main types of telescopes and their advantages and disadvantages.
At the beginning of the 17th century, In Netherlands, The first known practical telescopes were invented, and they were “refracting telescopes”.
A telescope is a complex optical device, by using it, you can see distant objects (astronomical or terrestrial) in multiple magnifications.
Structurally, it is a tube, at one end of the tube, it has a light collecting lens (concave mirror) and on the other side, it has the eyepiece, so that, You can only focus on the resulting image.
A simple telescope design includes,
- Search for the discovery of specific astronomical objects
- Light filters that mute very bright stars
- Diagonal mirrors (correction plates), where the lens sends “upside down”
Professional Telescope models with astrophotography and video capabilities can be augmented by the following elements,
- Sophisticated Electronic Equipment
- GPS System
- Electric Motor
The 3 Main Types of Telescopes
Refractor Telescope (LENS)
The lens and the eyepiece in the Refractor Telescopes are on the same axis, and the enlarged image is captured in a straight line.
Refractors or Refracting telescopes have collected the reflected light of the celestial bodies with the help of 2-5 biconvex lenses spaced on both ends of the long tube.
This type of telescope is more suitable for beginners and astronomers, as it allows for a good look at the terrestrial objects and celestial bodies within our solar system.
The lenses installed in the refractors decompose, the light “caught” by the lens into spectral components, leading to some loss of image clarity and making it dimmer with too much magnification.
It is recommended to use such a telescope in open areas, like outside of the city, where lighting in the sky is minimal.
Advantages and Disadvantages of Refractor Telescopes
- Easy to use and does not need special maintenance
- The sealed design is protected from dust and moisture
- No issue comes in temperature changes
- They provide a clear, contrasting and close picture of the astronomical body
- Have a long service life
- Large and heavy (some big models weigh up to 25 kg)
- Maximum lens diameter 150 mm
- Not suitable for city observations
Depending on the type of lens installed, the refracting telescopes are divided into two types, Achromatic Telescope and Apochromatic Telescope.
- Achromatic Telescope uses achromatic lens. It goes for a small and medium degree of increase, but give a flat picture.
- Apochromatic Telescope makes the image more convex, but remove defects such as a fuzzy outline and the manifestation of the second spectrum.
Reflector Telescope (Mirror)
The Reflector Telescopes captures and transmits light beams using two concave mirrors.
One concave mirror is in the tube lens and the other reflects the image at an angle transmitting it to the naked eye.
Unlike a Refractor Telescope, Reflectors Optics are more adapted for studying deep space and obtaining a high quality image of distant galaxies.
The production of mirrors is cheaper than lenses, which affects on the cost of the devices. However, it is difficult for a beginner or a child to cope with complex settings and image corrector.
Advantages and Disadvantages of Reflector Telescopes
- The simplicity of the design
- Compact size and light weight
- Completely captured the dim light of distant cosmic bodies
- Large aperture (from 250 to 400 mm), giving a brighter and clearer picture with no defects
- Lower prices compared to similar refractors
- It takes time and experience to set up
- Dust or dirt can enter in the open design of the device
- Temperature changes can impact
- It is not suitable to observe the terrestrial and adjacent objects of the solar system
Catadioptric Telescope (Mirror Lens)
The Catadioptric Telescope is a combination of Refractor telescopes and Reflector telescopes.
The catadioptric telescope lens is built from lenses and glass, so it combines their advantages and compensates for the defects as much as possible with the help of the special plate corrections.
Catadioptric Telescope shows the image of both distant and neighboring astronomical objects perfectly, it allows not only to see the stars, but also to produce high quality images.
Advantages and Disadvantages of Catadioptric Telescope
- Compact dimensions and transportability
- Equally suitable for observing objects deep and close to space
- Give the highest image quality
- Aperture up to 400 mm
- High cost
- Long term thermal stabilization of air inside the tube
- Complex construction
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