Why Are Most Large Telescopes Reflectors, Not Refractors

Why Are Most Large Telescopes Reflectors, Not Refractors?

In astronomy, a telescope is a device that aids in the observation of remote objects by collecting electromagnetic radiation (such as visible light). The first practical telescopes were invented in the Netherlands at the beginning of the 17th century. They found use in both terrestrial applications and astronomy.

A reflecting telescope uses an arrangement of mirrors to collect and focus light, whereas a refracting telescope refracts or focuses light using lenses.

Why Are Most Large Telescopes Reflectors, Not Refractors?

The reason why most large telescopes are reflectors is because they are light and inexpensive. They can be made in almost any shape or size, and generally offer a large-aperture size for the least weight. The mirrors arrive at the telescope site pre-polished to a perfect parabola. The primary mirrors used on reflecting telescopes are either concave or parabolic, whereas that of refracting telescopes can also be made into spherical or hyperbolic shapes.

Reflecting telescopes use mirrors to collect and focus light, whereas refracting telescopes use lenses. The difference between the two is that lenses bend light on its path while mirrors reflect it. The principal purpose of a telescope mirror is to reflect light in order to collect and focus it on an eyepiece or camera lens rather than letting it pass through. A reflecting telescope uses a parabolic mirror whereas refracting telescopes typically have elliptical mirrors because they are more efficient at collecting and focusing light onto an eyepiece or camera lens.

Mirrors are able to focus a greater amount of light onto a smaller region than lenses. They can be made in a variety of sizes and shapes, and generally have larger aperture diameters than refractors. Large aperture diameter provides a large observation area which is important for research observations. However, they are also much heavier than refractors because they require an extensive framework to support the mirror. This makes them more expensive to transport and less mobile for use in different locations.


In conclusion, mirrors are used on reflecting telescopes because they are light and inexpensive, whereas for refracting telescopes glass lenses/polymers can be used as key elements.

As a result of the large aperture size, large amounts of light can be collected before it is focused onto an eyepiece or camera lens. In doing this, they are able to significantly improve visual clarity of astronomical objects. This is important to achieve adequate resolution for scientific research observations and achieve excellent image quality at high magnifications.


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