The aperture of a telescope is made large,because

In a Galilean telescope,if the powers of an objective and eye lens are respectively $+1.25 \, D$ and $-20 \, D$,then for relaxed vision,the length and magnification will be

In an astronomical telescope in normal adjustment,a straight black line of length $L$ is drawn on the inside part of the objective lens. The eyepiece forms a real image of this line. The length of this image is $I$. The magnification of the telescope is:

If a telescope is reversed,i.e.,viewed from the objective side,what happens to the appearance of the object?

$A$ terrestrial telescope is made by introducing an erecting lens of focal length $f$ between the objective and eyepiece lenses of an astronomical telescope. This causes the length of the telescope tube to increase by an amount equal to

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: