A Newtonian reflecting telescope has a concave primary mirror of focal length 2.0m. A plane secondary mirror is located 18cm in front of the primary focus and sends the converging beam sideways to an eyepiece of focal length 25mm arranged for normal adjustment.
(i) Calculate the angular magnification produced by the telescope.
(ii) Determine the straight-line distance from the vertex of the primary mirror to the centre of the eyepiece along the main axis of the instrument.
(iii) Compare the distance obtained in part (ii) with the focal length of the primary mirror and briefly comment on why reflecting telescopes can be physically shorter than their focal length.