Telescopes

Optical and radio telescopes

A refracting telescope in normal adjustment has angular magnification $M=\frac{f_o}{f_e}$ and length $f_o+f_e$. Reflectors use curved mirrors and avoid chromatic aberration. A telescope's resolving power is limited by diffraction, $\theta\approx\frac\lambda D$; its collecting power is proportional to $D^2$. CCDs record images far more efficiently than the eye or film.