Refracting telescopes are also known as refractors, because they use the refraction principle to bend light through their lenses (curved primary lens and eyepieces).
The lenses can have different shapes: convex, concave, or plane-parallel and in turn can have more than one component in their configuration.
As a curious fact, refractor telescopes were the first to be used for astronomical observation and its technology was developed by Galileo in 1609.
Galileo with his modest instrument was the first to explore systematically the valleys and mountains of the Moon, as well as the phases of Venus.
During the centuries after its invention, refractors continued to have development. In 1897, the largest refracting system in the world was built and installed at Yerkes Observatory. This telescope has 1-meter (40-inch) diameter aperture.
Fortunately for you, there are very good refracting telescopes on the market. So we will inform you about the main aspects of choosing the best refractor based on your needs and budget.
Best refractor telescopes – Summary Table
If you are in a hurry, here we choose the top refracting telescopes:
|Celestron Advanced VX 6" f/8 Refractor Telescope|
|Orion 9534 ED80T CF Triplet Apochromatic Refractor Telescope|
|Sky-Watcher ProED 100mm Doublet APO Refractor Telescope|
|Orion 9005 AstroView 120ST Equatorial Refractor Telescope|
|Meade Instruments StarNavigator NG 102MM Refractor Telescope|
|Sky Watcher Evostar 72 APO Refractor Telescope|
What are the features of a good refracting telescope
To buy a telescope refractor, you must first consider some essential features. The variation of them will make your viewing experience different.
Let’s review the features that will make your first refractor a lifetime gift.
The opening of your refracting telescope should be large enough to capture as much light as possible. A larger lens results in better-magnified images, sharper and brighter.
A 6-inch refractor is a starting point on choosing the best one.
The focal length is an important feature on choosing refractor telescopesforsale. This feature is the length of the telescope and determines how far you will see the telescope, its field of view and the amount of chromatic aberration.
A long focal length shows the larger objects, but with a narrower field of view. On the contrary, with a short focal length, you have a wide field of vision but the objects look smaller.
Although not always applicable, to observe the Moon and the planets it is necessary to have longer focal lengths. So for star fields, it is better suited to shorter focal length.
For a beginner with a refracting telescope, approximately an aperture/focal length ratio of 10: 1 is adequate. Let’s say, a focal length of around 1000mm to 1200mm and a minimum aperture of 90mm will give you versatile results, however, it will depend on your preferences of space observation.
Portability will be affected by the robustness of the pieces in terms of performance, size and construction material.
The focal length also plays into the portability of the telescope. A large focal length involves a large telescope, but if it is short, it will require eyepieces to correct the field curvature. That would be an element and additional weight to the telescope.
Taking a balance with the focal length is fundamental, so the f/8 represent a versatile size.
Likewise, the telescope’s portability goes as long as it does not weigh more than half the weight of the user. In any case, its weight should not be greater than 50kg.
Refractors: Pros & Cons
Good refracting telescopes have a series of advantages and disadvantages compared to other models. Therefore, we list them:
Pros of Refracting Telescopes
In general, these telescopes have the following advantages
- Telescope par excellence for the observation of the Moon and the planets of the Solar system.
- Superior ease of use compared to other types of telescope.
- Offer better contrast than reflectors.
- Maintenance is almost nil because of its configuration and design.
- Collimation and alignment of optics disappear.
- Reduction of future expenses for maintenance, improvement or restoration of the telescope.
Cons of Refracting Telescopes
Now you must weight the refractor’s disadvantages:
- They are not good for deep-sky observation.
- They are heavier, they need bigger lenses and longer apertures.
- Under similar performance tend to be more expensive.
- Refractors often suffer from chromatic and spherical aberration.
Types of Refractor Telescopes
There are several types of refracting telescopes for the development they have had since their invention.
The types of refractor telescopes were given by the evolution they had, which can be summarized in 5 stages:
- The Galilean Telescopes made use of concave lenses.
- The Keplerian telescope that possessed of convex lenses.
- Achromatic refractors, which use two-piece lenses that will bring light of two different frequencies to a common focus in order to reduce chromatic and spherical aberration.
- Apochromatic refractors possess an additional lens compared to the Achromatics, so the aberration will be lower.
- Multilens telescopes, which can be used for more than a few lenses for even better reduction of aberration.
So, the types of refractor telescopes are: achromatic and apochromatic. But these configurations can also have multiple lenses: Doublet, Triplet, and Petzval Telescopes.
Each type of telescope reduces the chromatic and spherical aberration in a different way. Let’s see what characteristics each of them has.
They are the cheapest refractor telescopes on the market, because they have almost no coating that eliminates chromatic aberration. Because of its configuration, the frequency of observing sessions with reasonable seeing conditions tends to be higher. They are good for solar observing.
These types of refracting telescopes have better correction of chromatic and spherical aberration than the much more common achromatic lenses. The lenses bring light of three wavelengths (typically red, green, and blue) into a common focus in the same plane. Apochromats correct spherical aberration at two wavelengths, rather than one as in an achromat. That is, you will get a cleaner view at the night sky.
To catch more light in the telescope, it is necessary to increase its size. A larger telescope is more expensive. An optimal solution is a telescope with multiple lenses that correct the chromatic aberration, giving the user a much cleaner view than the other scopes.
They have very fast focal ratios, and they are the easiest to use in astrophotography. We recommend these telescopes to the serious astrophotographers.
Using a Refractor Telescope
The operation mode of a telescope refractor is quite simple, after the first time and with a little practice, you will be very comfortable using it.
In general, the operating procedure of a refractor is as follows:
- Choose an observation site away from sources that illuminate the night sky.
- Place the tripod on the ground and adjust its legs to the same length.
- Insert the telescope into the tripod mounting bracket.
- Insert the finder scope into the frame provided for it.
- To have a point of reference, aim the telescope at a bright celestial object that is of your knowledge.
- Move the telescope tube in the corresponding directions to aim at the astronomical objective of your interest.
- Look through the finder scope.
- Adjust the orientation of the telescope to center the object in the finder scope.
- Insert the eyepiece into the telescope’s focuser.
- Look through the eyepiece and confirm that the object is in the field of view.
- Centers the object with the scope finder.
- Adjust the focuser knob to sharpen the object in the eyepiece.
- Repeat the process for new observations.
Refracting Telescope Facts
When you go to buy your first refractor telescope it is worth knowing a little general culture:
- The largest Galilean Telescope was only about 47 inches long and had an opening diameter of 2 inches.
- Galileo’s Telescope had 30X magnification.
- In 1877, the astronomer Asaph Hall discovered the two moons of Mars, Phobos, and Deimos.
- The refractor telescope used by Asaph Hall measured 26 inches and can still be used to observe binary stars.
- Refractors over 40 inches long are difficult to use.
- Refractors are less common in astronomical observatories than reflecting telescopes.
- In general, astronomical observatories that have refracting telescopes, use equatorial mountings.
- Refractors can be mounted on either Equatorial or Altazimuth mount.
- Inside they have two types of lenses: concave and convex.
- Greater separations between the concave and convex lens will make the image clearer.
- Refractors are popular among serious astrophotographers.
- They are the best for beginners, mostly due to their ease of use and low maintenance.
- The largest refractor telescope in all observatories in the world is at the Yerkes Observatory in Williams Bay.
- 1 meter is the opening diameter of the largest refractor telescope in the world.
- The refracting telescope in Wisconsin (Yerkes Observatory) was built and installed at the end of the 19th century.
- The second largest is at the Lick Observatory in California, measuring 36 inches.
- The Lick Observatory Refracting Telescope is 57 feet long, 4 feet in diameter, and weighs over 25,000 lbs.
- Lick Refractor allowed to discover Jupiter’s fifth moon