How do Refracting Telescopes work?

An optic scheme of a refracting telescope

A refractor, or a lens telescope, is the oldest type of telescopes. It was invented in 1609 by Galileo Galilei and was updated in consequence. Firstly, a refractor used two lenses: convex as an objective and concave in an eyepiece, that caused spherical and chromatic aberrations. This scheme was supplemented by a second lens of different sorts of glasses in the objective to avoid visual distortions. Now, an achromatic refractor it`s a classic at astronomy: it gives a good image and doesn`t take too much money. If you want the best quality of image, then you should pay attention to an apochromatic refractor. In this case, the objective has already three ultralow dispersion glasses and provide a clear image that is free of aberrations.

How refracting telescope works?

Any type of telescopes works like our eye: it gathers the light and focuses it in one point – in an eyepiece. The lighter an object – the better the image. Different design types are intended to reduce the distortions of the image. A refractor design is the oldest and easiest at the same time. It consists of an objective lens, which collects the light, and an eyepiece.

An achromatic refractor has in its objective two lenses of different sort of glasses, that helps to reduce chromatic aberrations.

Achromatic refractor scheme

An apochromatic refractor uses two or three lenses, which were made of ultralow dispersion glasses or of fluorite.

Apochromatic telescope scheme

Advantages of refracting telescopes:

  • Their lenses are covered by a telescope`s case, so they are protected of dust
  • Their lenses are set up during production, so you do not need to be engaged in an adjustment
  • They give contrast and colorful image
  • Reliability thanks to the simplicity of a design
  • They are good for solar system planets, for the Moon and binary stars

Disadvantages of refracting telescopes:

  • Powerful refractors are more expensive than two other types
  • Long focal length causes bulky design
  • Not good for deep sky
  • Chromatic aberrations

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