Refracting telescope (Keplerian and Galilean)
A telescope that uses only the refraction of a lens is called a refracting telescope. There are two types, the Galilean telescope and the Keplerian telescope. The Galilean telescope or earth telescope consists of a convex objective and a concave eyepiece. The Keplerian telescope has a convex objective and convex eyepiece. Most astronomical telescopes in use today are Keplerian telescopes.
Reflecting telescope (Newtonian)
The condensation of a telescope is closely related to the size of the objective lens. This leads to a preference for larger telescopes. However, refracting telescopes cannot be made as large as desired. The telescope that solves this problem is the reflecting telescope, which is currently the most widely used telescope for astronomical observation.