The magnifying power of a refracting type of astronomical telescope is $m$. If the focal length of the eyepiece is doubled,then the magnifying power will become:

$A$ reflecting telescope utilizes

Write a note on Cassegrain telescope.

For a telescope in normal adjustment,the length of the telescope is found to be $27 \, cm$. If the magnifying power of the telescope at normal adjustment is $8$,the focal lengths of the objective and the eyepiece are respectively:

$A$ Cassegrain telescope uses two mirrors of radii of curvature $25 \ cm$ and $16 \ cm$ separated by a distance of $2.5 \ cm$. The position of the final image of an object at infinity is

In a laboratory,four convex lenses ${L_1}, {L_2}, {L_3},$ and ${L_4}$ of focal lengths $2 \ cm, 4 \ cm, 6 \ cm,$ and $8 \ cm$ respectively are available. Two of these lenses form a telescope of length $10 \ cm$ and magnifying power $4.$ The objective and eye lenses are: