`(a)` Draw a labelled ray diagram to obtain the real image formed by an astronomical telescope is normal adjustment position. Define its magnifying power.
`(b)` You are given three lenses of power `0.5 D`, `4D` and `10D` to design a telescope.
`(i)` Which lenses should be used as objective and eyepiece? Justify your answer.
`(ii)` Why is the aperture of the objective preferred to be large ?