The Lens Maker's Formula relates the focal length ($f$) of a lens to its physical properties: $\frac{1}{f}=(n_{rel}-1)\left(\frac{1}{R_1}-\frac{1}{R_2}\right)$

• $n_{rel}$ is the refractive index of the lens material relative to the surrounding medium.
• $R_1,R_2$ are the radii of curvature of the two lens surfaces.
• Proper sign conventions must be used for $R$ (e.g., $R$ is positive if the center of curvature is on the side of the outgoing light).