Telescope is an optical instrument that uses optical devices such as lenses or mirrors to observe distant objects. The light passing through the lens is refracted or reflected by concave mirror into the pinhole to converge and image, and then it is seen through the magnifying eyepiece.

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 much thicker than the pupil diameter to the human eye, so that the observer can see dim objects that were not seen before.

Extended data:

galileo telescope

The objective lens is a convergent lens and the eyepiece is a telescope with a divergent lens. The real image formed by the refraction of light through the objective lens is in the focus behind the eyepiece (near the back of the human objective lens). This image is a virtual image to the eyepiece, so it is refracted by the eyepiece to form an enlarged upright virtual image. The magnification of galileo telescope is equal to the ratio of the focal length of the objective lens to the focal length of the eyepiece.

Kepler telescope

This principle consists of two convex lenses. Because there is a real image between them, the reticle is easy to install and has excellent performance, so military telescopes, small astronomical telescopes and other professional telescopes all adopt this structure. But the imaging of this structure is inverted, so an upright system should be added in the middle.

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