In a Galilean telescope,the final image formed is:

To increase the magnifying power of a telescope ($f_o$ = focal length of the objective and $f_e$ = focal length of the eye lens):

In a terrestrial telescope,the focal length of the objective is $90\, cm$,the inverting lens is $5\, cm$,and the eye lens is $6\, cm$. If the final image is formed at $30\, cm$ from the eye lens,calculate the magnification.

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

$A$ telescope has an eyepiece of focal length $5\, cm$ and an objective lens of focal length $60\, cm$. It is focused on a distant object such that the rays emerge from the eyepiece as parallel rays. Find the angular width of the image in degrees $(^o)$ if the object subtends an angle of $2^o$ at the objective.

If the tube length of an astronomical telescope is $105 \, cm$ and the magnifying power is $20$ for normal setting,calculate the focal length of the objective in $cm$.