What kinds of lens structures are there in astronomical telescopes?

Optical astronomical telescopes are divided into reflective, reflective and catadioptric astronomical telescopes.

As the name implies, refractive telescopes use the principle of refraction of light to gather light. Early telescopes usually used convex lenses, but this brought color difference problems.

The dispersion of light knows that the refraction angles of light with different frequencies are different after passing through the lens, so when the light passes through the refractive telescope, there will inevitably be color difference, which is manifested in the appearance of purple at the edge of the object.

In order to solve this problem, people use a variety of lens combinations to reduce the chromatic aberration to a certain extent, and now the chromatic aberration of a good refractive telescope has been reduced to a negligible level. However, due to the use of a variety of lenses, its price is relatively high. Its advantage lies in its sharp imaging, which is beneficial to celestial photography.

Reflective telescope uses the principle of light reflection to gather light. Because the reflection principle is adopted, there will be no color difference problem. However, compared with refraction, the objective lens of reflective telescope has a secondary mirror besides the primary mirror, which generally blocks the light path.

In addition, the imaging of reflective telescope is very sensitive to the optical axis and accuracy, and the lens barrel is open, which is easy to dust and needs to adjust the optical axis, which may be a bit difficult for novices. But its advantage lies in its low price and large caliber.

Extended data

The first function of the telescope is to enlarge the opening angle of distant objects, so that the human eye can see the details with smaller angular distance. The second function of the telescope is to send the light beam collected by the objective lens, which is much thicker than the pupil diameter (up to 8 mm), to the human eye, so that the observer can see dim objects that he could not see before.

1608, Hans Justus Hans Liebig, a Dutch optician, accidentally discovered that two lenses could be used to see the distant scenery. Inspired by this, he made the first telescope in human history. 1609 Italian Florentine Galileo Galili Lei Faming made a 40x telescope, which is the first practical telescope put into scientific application.

Baidu encyclopedia-telescope