Transcript of how to choose your telescope

 

GUIDE HOW TO CHOOSE YOUR TELESCOPE

A telescope collects light from very distant objects; therefore, the most important factor is the aperture; with more light we will have more definition, more magnification and more objects to observe. However, larger opening implies larger size, greater assembly complexity, weight and cost. The ideal is to choose according to your needs such as frequency of use, portability and price.

REFRACTOR TELESCOPE

The objective is a lens (loupe type) located at the beginning of the tube, where the light is “refracted” and magnifies it to the eyepiece located at the other end of the tube.

It is recommended for any level due to its ease of use, but there are also advanced ones with apochromatic or ED glass. (low dispersion) glass, aimed at experienced observers.

ADVANTAGE:
  • They are more practical and easier to use, especially in terrestrial observation.
  • In small openings they are cheaper, resistant and do not need maintenance.
DISADVANTAGES:
  • The larger the aperture, the more expensive it is than a reflector.
  • Limited in observation of Nebulae and Galaxies.

REFLECTOR TELESCOPE

Also called Newtonian, they use a concave mirror located at the bottom of the light tube, where it is “reflected” and amplified towards another small mirror. (secondary) Located in the opening, and then reach the eyepiece, which is located at the side of the tube. This Telescope is recommended at an amateur or semi-professional level. They are also available with parabolic mirror (wider mirror) for the more experienced.

ADVANTAGE:
  • Allows larger aperture at a good price. Excellent for Nebulae and Galaxies. They are lighter and more manageable in spacious places.
DISADVANTAGES:
  • More delicate, due to the exposed mirror.
  • Slight loss of light due to obstruction of the second mirror.
  • In some cases, it is necessary to collimate (align) the mirror.
  • Uncomfortable for terrestrial observation.

CATADIOPTRIC TELESCOPE

These telescopes combine the characteristics of the previous ones, the light is amplified in a concave mirror (donut type) that is located at the bottom of the tube and then passes through a corrector lens that is in the opening, returning the light to reach the eyepiece, which is located at the rear of the tube. Generally, they are recommended for people who have experience in the use of telescopes.

ADVANTAGE:
  • Good performance on faint bright or terrestrial objects.
  • Enables higher magnifications in a smaller tube.
  • The tube is closed and protects the inner optics. Comfortable to carry.
DISADVANTAGES:
  • They are the most expensive on the market.
  • Loss of light due to obstruction of the corrector lens.
  • In large models, the tube is usually very heavy.
  • Maintenance and disassembly are usually more delicate and complex.

FRAME TYPES

The mount is a key element in the telescope as it provides support and stability, while at the same time directing the telescope to the desired position. It is important to consider that the larger the aperture, the heavier and more stable the mount will need to be, in order to avoid undesirable vibrations at high magnifications.

AZIMUTH

These mounts have two axes, one vertical and one horizontal (up and down), making the telescope easy to handle. Ideal for children and beginners, basically, is to point and observe, they are cheaper and very portable. They are also a great help with moving objects. The disadvantage is that they are not good for incorporating motors (especially used in astrophotography), nor for supporting large apertures.

EQUATORIAL

They have two axes, but one of them is positioned according to the tilt axis of the earth (located parallel to it). With these mounts, it is easier to track the stars. If motorized, long exposure astrophotography is possible. It is also more stable because of its weight. However, because of its weight and mounting accessories, it is less portable, and handling is more complicated than the azimuthal, but with practice you will acquire great fluency and better results.

COMPUTERIZED GOTO

Computerized mounts do most of the work, which means that they move to where you must point and follow the object according to the rotation of the Earth. To use this mount, you must know a few stars, as it must be aligned. This alignment process is vital for the telescope to point well, otherwise it would be like having an azimuthal telescope. It can be used by amateurs to make their observation more comfortable, although they are usually used by experienced astrophysicists.

DOBSONIAN

Commonly called “Dobson”. They are very easy to use and allow large apertures at a good price. However, because they are at ground level, they are the most uncomfortable for terrestrial observation or astrophotography, and their design makes them less portable. There are also motorized ones, although the price for this factor is quite high. So, it is recommended for lovers of large apertures who enjoy observing without leaving home.

EYEPIECES

The eyepiece is a fundamental part of the observation, as the quality of the image we see will depend on it. They are usually labeled with a measurement (expressed in millimeters) that indicates the size of the internal glass. The larger the size, the lower the magnification, but the higher the brightness and field of view (necessary for faint objects). There are several types, and these depend on the number of lenses to improve the image and the field of view to enlarge the vision (expressed in degrees). The most commercial ones are the following:

1.HUYGENS

They are eyepieces with 2 internal lenses and low quality. It is common in children’s telescopes. It has the smallest field of view (less than 40º) and being one of the smallest, the compatibility with other telescopes and accessories such as filters is scarce, but sufficient for Moon and terrestrial observation.

2. KELLNER

They consist of three lenses. These Eyepieces are recommended for beginners or for Telescopes with medium apertures. They do not suffer from chromatism and have a field of view of little more than 40º. A variant of these are the modified achromatic (MA). They perform well in observing Planets, the Moon and stars.

3. PLÖSSL

Built with four internal lenses and perfectly machined. They improve the contrast on planets, and thanks to their 50º field of view, with a large diameter, they facilitate the observation of nebulae and galaxies. A variant of this eyepiece is the Super Plossl (SP) and can reach 52º field of view.

4. Nagler o 2 Pulgadas

Dedicated to experienced observers with an advanced telescope and requiring extraordinary detail. Due to its large field of view, it allows you to see faint objects or several objects at the same time. Not all telescopes accept this type of eyepieces, as some are usually more expensive than the telescope itself.

POWER OR MAGNIFICATION

Telescopes are not measured by magnification, because the eyepieces are used to obtain various magnifications. However, there are 2 factors that can measure the power or magnification of each telescope:

TELESCOPE DIAMETER (APERTURE)

It is a useful reference to determine the maximum magnification without deteriorating the quality of the observed object. If this limit is exceeded, the image will start to deteriorate significantly.

For a simple example, the power of a telescope will have as reference the double of its aperture (expressed in millimeters), this means that, if a Telescope measures 50mm, the maximum magnification would be 100x, (50 times 2 equals 100x); or a 76mm Telescope will have a maximum of 152 magnifications.

MAGNIFICATION WITH EYEPIECES

Magnification is not the number of times an object appears larger; it actually indicates how we would see the star if we were located at a distance x times closer. The following formula is used to calculate the magnification we are using:

Magnification = Focal length of telescope / Focal length of eyepiece.

In other words, divide the length of the tube (F) by the size of the eyepiece (mm). Example, we have a telescope with 750mm focal length and a 25mm eyepiece.

Magnification = 750 / 25 = 30x

With the above, we have a telescope with a 750mm long tube, and a 25mm eyepiece, we get 30 magnifications. If to the same telescope we put a 10mm eyepiece, then we would have 75x. (750/10=75). ). And furthermore, if to this last example we add a 2x Barlow, we would have 150x. (75×2= 150).

BARLOW LENS

It is an interchangeable lens that is placed between the Telescope and the Eyepiece to obtain greater focal length (F), and consequently, achieve more magnification. There are several types and brands. The most common are the 2x, and like everything else, the better the quality of the lens, the better the magnification, so they are usually sold individually.

With the use of the Barlow, it must be considered that, like all light passing through a second lens, the quality of the image and the field of view is reduced. Therefore, it is recommended to use it in Telescopes with short focal lengths and to observe bright objects such as the Moon, some Planets and Stars.

IDEAL INCREASE

While it is true, one can go beyond the maximum limit of a Telescope, either with a powerful eyepiece or a Barlow lens. However, at higher magnification, the field of view is reduced, and the image becomes fuzzy, dark and the objects under observation will move quickly. Therefore, the ideal is to have a balance between magnification and image quality.

FINAL RECOMMENDATIONS

Considering the above, the best Telescope is the one you use the most. If you are passionate about astronomy we suggest investing in a large Telescope; if you are casual and enthusiastic, a medium Telescope; if you are a curiosity or a gift, a portable Telescope. However, we give the latest recommendations gathered by amateurs and less expert sources for a good choice.

  • Observe first with Binoculars. Several (inexpensive) Telescopes have the same performance as a binocular, so if you can observe first with Binoculars, it would be a great way to decide if you are curious and invest in a Telescope.
  • You will not see pictures like in magazines. Unfortunately, most of these beautiful images are taken with institutional equipment, or out of Earth orbit. In addition, they are taken with fancy sensors, long exposure and edited (Photoshop type), to achieve a spectacular environment.
  • Do not choose by magnification. In the market there are telescopes with basic apertures (50 – 60mm) that promise high magnifications, which is impossible, being only a marketing act to sell. In the end you will be disappointed.
  • Include several eyepieces. The more, the better, since in astronomy the objects are appreciated of different size, intensity and color. If they are included in the Telescope, you will have significant savings than buying them individually.
  • Brands.There are many brands, but do not get carried away by the first one, as most Telescopes are manufactured by the same Chinese company (as well as Smartphones). Nor by generic Telescopes “made up” with printed labels and promising wonders. Be cautious.
  • Internal Barlow. Some telescopes (mainly reflectors) include an internal lens that cannot be removed, making the optical tube shorter, reducing space. However, they reduce the field of view and do not allow more utilities, such as astrophotography. However, they reduce the field of view and do not allow more utilities, such as astrophotography. Avoid these teams.
  • Apps. Currently there are several applications for Smartphone that will help you locate objects easily with the Telescope, i.e. just by directing the Telescope as indicated by the application, you will locate any object. If possible, join astronomical clubs and communities, which will give you tips and invaluable information.