How does a telescope work?

Knowing how a telescope works is very important when we want to see objects that are at great distances. Continue reading this article and you will get all the necessary information.

A telescope works thanks to curved mirrors and convex lenses located in such a way that it allows the observation of objects at great distances such as stars, planets and even galaxies. Currently, they allow to observe beyond visible light.

To understand how this tool works, it is necessary to know the configuration of Galileo and Kepler, which in both cases use the refraction of light to achieve increased observation of distant objects.

Basically in both models there is a first lens, which is called the objective lens, where the rays coming from the object converge in parallel to meet at a distance equal to the focal length, and the second lens called the eyepiece is the one that produces the final image , which is the result of the target.

Galileo Galilei Configuration

In 1609, Galileo introduced the first telescope to be used as an astronomical instrument. This had two lenses, the objective lens that was closest to the converging object and the eyepiece that was closest to the diverging eye. Thanks to this, virtual and augmented images could be obtained. It is worth noting that they could be used for terrestrial observations.

Setup by Johannes Kepler

By 1611, the eyepiece of a converging lens was used for the first time to be able to observe objects at great distances. The objective shows a first image thanks to the rays that arrive parallel to the first lens, it is located in the focus, which increases its angle like a kind of magnifying glass. This allowed a more detailed look at the target.

This model served as the basis for what is now known as a retractor telescope, which is used in today's cameras, with modifications in the prismatic part.

Parts of a telescope

Telescopes work from a lens and others from a mirror, both with the sole intention of capturing as much light as possible. This is called an objective, which has a diameter or aperture causing light to be concentrated at the opposite end of the optical tube. This tube can be made of cardboard, fiber or metal, among others.

The focus is the point where the light is concentrated, which in turn determines the distance or focal length. The larger the diameter, the greater the amount of light, which generates images with better sharpness. The telescope is capable of absorbing more light than the human eye, so dimmer and higher magnitudes can be perceived.

Types of telescopes

How telescopes work according to their classification and optical principles, will depend on how light rays propagate, that is, their reflection and refraction. For this reason, there are three types of telescopes: the refractor, the reflector or Newtonian and the catadioptric or mixed.

Refractor: It is based on the principle of refraction, that is, the image is formed from the deviation suffered by light rays when they pass through the lens. Thanks to this, greater sharpness and contrast of the image can be achieved. They are used to observe planets and the moon, but not for the deep sky, such as nebulae or clusters.

Reflector: Its optical principle is reflection, which consists of the rays emanating from the object being directed to the eyepiece through two curved mirrors that allow greater absorption of light. This is used to visualize deep sky objects, although it requires constant alignment in the mirrors, which becomes a great disadvantage.

Retroreflectors: Also known as mixed, this uses the principles of refraction and reflection, using both a lens and a mirror to direct the eye rays, which allows it to cover large focal lengths. It does not require maintenance, So it's totally sealed. Its disadvantage is that it loses a little light through the secondary mirror.

Telescope characteristics

Currently there is a wide variety of models that can meet the demand of fans, both in cost, size and function. All this will depend on the function you want it to fulfill. It must be made clear that perfect vision will never be achieved, which is why it is wrongly classified as a bad telescope.

To achieve an almost perfect degree of sharpness, it is necessary to use planetary probes, because their photographs are capable of capturing images that the human eye is incapable of conceiving.

Now then, chromatic aberrations are part of the functioning of telescopes, since they consist of those imperfections that occur in the lens and that throw an inconsistency between the real object and the image that is perceived. Reflecting and catadioptric telescopes usually present this defect, causing the focus to be distributed along the optical axis.

In the case of catadioptric telescopes, it usually presents an additional aberration which is the curvature of the field, where the sharp image is projected on a spherical rather than flat surface.

It must be taken into account that all telescopes invert the images according to the observer's disposition, this should not be taken as a defect but as an optical characteristic.

Most outstanding telescopes

There are a large number of telescopes or observation centers that perform a great observation function, especially in outer space. Among the best known is the Great Reflecting Telescope of the Canary Islands, which is the largest in the world, with a mirror of 10.4 meters in diameter divided into 36 hexagonal mirrors.

Followed this is the Keck Observatory on Mauna Kea (Hawaii), considered the second largest.

Currently, a large telescope is under construction whose main mirror will measure approximately 30 meters in diameter, more than twice the diameter of the one found in the Canary Islands, which will make it possible to make large observations like never before, and there is a prototype called European Extremely Large Telescope, which claims to measure 39 meters in diameter.

Curiosities about telescopes

Telescopes perform three primary functions: light gathering, resolution and magnification, allowing the human eye to see with the naked eye, including the spectrum of light beyond visible light, gamma rays, X-rays, ultraviolet rays , infrared rays, microwaves and radio waves.

The most expensive telescope in the world is the Hubble Space Telescope and its successor is the James Webb Space Telescope. Telescopes today are manipulated via remote computers and rarely look through the eyepiece.


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