In order to view distant objects clearly in their magnified form, the telescope is used and the telescopes used to see astronomical sources such as the stars and the planets are known as astronomical telescopes. There are two types of telescopes. They are:
1. Refracting telescope, which uses lenses and
2. Reflecting telescope that uses mirrors as well as lenses
In both the telescopes, the image formed by the objective is the object in the eyepiece, which produces the real image. Objective lenses are of large diameter and larger focal length so that the maximum amount of light coming from the distant object can be collected. However, the eyepiece is of smaller size with lesser focal length. Also, both the lenses fit inside a metallic tube in such a way that the distance between them can be changed. Meanwhile, the principal axes of both the lenses are on the same straight line. Generally, by using the same objective with different eyepieces, it is possible to get images with different magnification.