Source: /cirosantilli/focal-length

= Focal length
{title2=f}
{wiki}

If you pass <parallel light>.

For a <biconvex spherical lens>, it is given by:
$$
\frac{1}{f} = n \left( \frac{1}{R_1} + \frac{1}{R_2} \right)
$$
where:
* n: f nidnex