Question

Which type of telescope can be made using a concave mirror, convex mirror, plane mirror and a lens? Draw diagrams of these telescopes.

Answer 1

Reflecting types of telescopes can be made using a concave mirror, convex mirror, plane mirror and a lens. Reflecting type of telescopes is mainly of two types:
(a) $Newtonian$ telescope(Refer Fig.1)
Light rays coming from a heavenly body (distant object) get reflected by the concave mirror. Before the reflected rays converge at the focus of the concave mirror, it is again reflected by the plane mirror as shown. As a result, the rays pass through the eyepiece and we get a magnified image of the body.
(b) $Cassegrain$ telescope (Refer Fig. 2)
In this telescope, the light rays after reflection from the concave mirror, are reflected back towards it by a small convex mirror. Then the rays pass through the eyepiece placed at the back of the concave mirror as shown. The eyepiece produces ​a magnified image of the source.