Write a note on Cassegrain telescope.

(N/A) Cassegrain telescope uses a concave primary mirror and a convex secondary mirror to focus incident light. The light reflects off the primary mirror,hits the convex secondary mirror,and is then directed through a central hole in the primary mirror to the eyepiece.
This design is named after its inventor,Laurent Cassegrain.
The primary advantage of this configuration is that it provides a large focal length within a compact,short telescope tube.
The largest telescope in India is located in Kavalur,Tamil Nadu. It is a $2.34 \ m$ diameter reflecting telescope.
It was ground,polished,set up,and is being used by the Indian Institute of Astrophysics,Bengaluru.
The largest reflecting telescopes in the world are the pair of Keck telescopes in Hawaii,$USA$,with reflectors of $10 \ m$ in diameter.