Question

State the condition under which a large magnification can be achieved in an astronomical telescope.

Answer 1

Condition under which a large magnification can be achieved in an astronomical telescope:

In astronomical telescope, the light is incident from infinity on the objective lens and it forms image at the focus of the objective lens and for large magnification the length between the lens is so adjusted that the final image is formed at the least distance of the distinct vision from the eyepiece

Magnification of astronomical telescope is

\[(M . P )_\max = - \frac{f_o}{f_e}(1 + \frac{f_e}{d})\] To have large magnification power, \[f_o\] must be large as possible and \[f_e\] must be as small as possible.

Answer 2

By increasing the focal length of objective lens and at the same time keeping the focal length of eye peice  minimum we can increase the magnifying power of telescope