Question

You are given following three lenses. Which two lenses will you see as an eyepiece and as an objective to construct an astronomical telescope?

Lenses	Power	Aperture
$L_1$	$3D$	$8cm$
$L_2$	$6D$	$1cm$
$L_3$	$10D$	$1cm$

Answer 1

In an astronomical telescope,

The eyepiece has greater power while a smaller aperture. and, the objective has lower power with a longer aperture so, by using $4$ as objective and $L_3$ are eyepiece, the best possible magnification,

$m=\frac{P_e}{P_0}=\frac{10}{3}=3.33$ can be achieved.