Which are two main points important for an astronomical telescope?

The diameter of the moon is $3.5 \times 10^3 \, km$ and its distance from the Earth is $3.8 \times 10^5 \, km$. Find the angle subtended by the moon at the eye when viewed through a telescope. The focal length of the telescope's objective is $4 \, m$ and the focal length of the eyepiece is $10 \, cm$. The angle is .......... $^o$.

An astronomical telescope has an angular magnification of magnitude $5$ for distant objects. The separation between the objective and the eyepiece is $36 \, cm$. The final image is formed at infinity. The focal length $f_o$ of the objective and $f_e$ of the eyepiece are

What is the length of an astronomical telescope for normal adjustment?

$A$ telescope has an objective lens of focal length $144\, cm$ and an eyepiece of focal length $6\, cm$. Find the magnifying power of the telescope for normal adjustment.

The length of an astronomical telescope for normal vision (relaxed eye) ($f_o$ = focal length of objective lens and $f_e$ = focal length of eye lens) is