As shown in the figure:
Optical astronomical telescopes are divided into reflective, reflective and catadioptric astronomical telescopes.
As the name suggests, a refracting telescope uses the principle of refraction of light to gather light. Early telescopes generally used a convex lens, but this introduced a chromatic aberration problem.
Dispersion of light, we know that light of different frequencies has different refraction angles after passing through the lens. Therefore, when the light passes through the refracting telescope, chromatic aberration will inevitably occur, which is specifically reflected 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 chromatic aberration to a certain extent. Now the chromatic aberration of good refracting telescopes has been reduced to the point where it can be ignored. But because it uses a variety of lenses, its price is relatively high. Its advantage is that the image is sharp, which is beneficial to astronomical photography.
Reflecting telescopes use the principle of light reflection to gather light. Since it adopts the principle of reflection, there will be no chromatic aberration problem. But compared to refraction, the objective lens of a reflective telescope has a secondary mirror in addition to the primary mirror. This secondary mirror generally blocks the light path.
In addition, the imaging of reflecting telescopes is very sensitive to the optical axis and accuracy. The lens barrel is open, so it is easy for dust to enter, and the optical axis needs to be adjusted. This may be a bit difficult for novices. . But its advantage is that it is cheap and the caliber can be made very large.
Extended information
The first function of a telescope is to enlarge the angle of distant objects so that the human eye can see details with smaller angular distances. The second function of the telescope is to send the light beam collected by the objective lens that is much thicker than the pupil diameter (maximum 8 mm) into the human eye, allowing the observer to see faint objects that were previously invisible.
In 1608, Hans Liebersch, a Dutch optician, accidentally discovered that he could see distant objects clearly with two lenses. Inspired by this, he built the first telescope in human history. . In 1609, Galileo Galilei, a native of Florence, Italy, invented the 40-power double-mirror telescope, which was the first practical telescope put into scientific application.
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