An astronomical telescope has an objective and an eyepiece of focal lengths $40\, cm$ and $4\, cm$ respectively. To view an object $200\, cm$ away from the objective,the lenses must be separated by a distance of.....$cm$.

The focal length of the objective and eye lens of an astronomical telescope are $2 \, m$ and $5 \, cm$ respectively. The final image is formed at $(i)$ the least distance of distinct vision and $(ii)$ infinity. The magnifying power in both cases will be:

The minimum magnifying power of a telescope is $M$. If the focal length of its eye lens is halved, the magnifying power will become:

The magnifying power of an astronomical telescope is $8$. If the distance between the two lenses is $54 \, cm$,find the focal lengths of the eyepiece and the objective lens.

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:

$A$ distant hot air balloon subtends $0.25^o$ at the objective lens of an astronomical telescope. The image subtends $1.5^o$ at the eyepiece when viewed with a relaxed eye. The objective and eyepiece are in a $35 \ cm$ long tube. Find the focal length of the eyepiece lens in $cm$.