Converging and Diverging Lenses

Theory

In a thin lens, rays parallel to the axis converge at the focus (converging lens, $f>0$) or appear to diverge from it (diverging lens, $f<0$). Thin-lens equation: $\frac{1}{f}=\frac{1}{d_o}+\frac{1}{d_i}$; optical power $P=1/f$ in dioptres.

What to observe

• Top: the rays cross at F′ (real focus).
• Bottom: the rays spread as if coming from F (virtual focus).

Try this

• Replace the parallel beam with a point source at 2f from the lens.
• Rotate a lens.

Also available in: Lentes convergente e divergente (Português) · Lentes convergente y divergente (Español)