A refracting telescope has an objective lens of focal length $150,\mathrm{cm}$ and an eyepiece of focal length $30,\mathrm{cm}$. It is adjusted for viewing distant stars (final image at infinity). Calculate the angular magnification.

Step-by-step solution

1. For a telescope with the final image at infinity, the angular magnification is $M=-\frac{f_o}{f_e}$.
2. Substitute $f_o=150,\mathrm{cm}$ and $f_e=30,\mathrm{cm}$: $M=-\frac{150}{30}=-5$.

Concept tested: Angular magnification of a telescope

Published 10 October 2026 · How this solution was prepared and checked