Question

Draw a labelled ray diagram of a refracting telescope. Define its magnifying power and write the expression for it.
Write two important limitations of a refracting telescope over a reflecting type telescope.

Answer 1

Refracting telescope :

Magnifying power : The magnifying power is in the ratio of the angle `alpha` subtended at the eye by the final image to the angle `beta` which the object subtends at the lens or the eye.
`m ~~ (beta)/(alpha) ~~ (h)/(f_(e)).(f_(0))/(h)=(f_(0))/(f_(e))`
Limitations of refracting telescope over reflecting type telescope -
(i) Refracting telescope suffers from chromatic aberration as it uses large sized lenses.
(ii) The requirements of big lenses tend to be very heavy and therefore difficult to make and support by their edges.