For an astronomical telescope,the focal length of the objective lens is $f_{0}$ and the eyepiece lens is $f_{e}$. Then the tube length of the telescope is . . . . . . .

The objective and eyepiece of an astronomical telescope are double convex lenses with refractive index $1.5$. When the telescope is adjusted to infinity, the separation between the two lenses is $16 \,cm$. If the space between the lenses is now filled with water and the telescope is again adjusted for infinity, then the present separation between the lenses is: (in $\,cm$)

$A$ simple telescope, consisting of an objective of focal length $60\, cm$ and a single eye lens of focal length $5\, cm$, is focused on a distant object in such a way that parallel rays emerge from the eye lens. If the object subtends an angle of $2^o$ at the objective, the angular width of the image is........$^o$.

The magnifying power of an astronomical telescope for relaxed vision is $16$. On adjusting,the distance between the objective and eye lens is $34\, cm$. Then the focal length of the objective and eye lens will be respectively:

The focal length of the objective of an astronomical telescope is $1.5 \ m$. Under normal adjustment,the length of the telescope is $1.56 \ m$. The focal length of the eyepiece is: (in $m$)