A student is analysing the design parameters of a Newtonian reflecting telescope in which a concave primary mirror forms an image that is viewed through an eyepiece kept in normal adjustment.
(i) State the expression for the angular magnification of the telescope when the final image is at infinity, clearly identifying the symbols used.
(ii) Explain qualitatively how the magnification will be affected in each of the following two independent changes:
(a) the focal length of the primary mirror is increased while the eyepiece remains the same,
(b) the focal length of the eyepiece is decreased while the primary mirror remains the same.
(iii) Give any two physical reasons why reflecting telescopes are generally preferred over refracting telescopes for achieving very high magnification in astronomical observations.