• Tags: lens, formula, lens-maker
• Difficulty: Moderate

Thin lens formula: 1/v - 1/u = 1/f

Lens maker's equation: 1/f = (n_{2}/n_{1} - 1)(1/$R_{1}$ - 1/$R_{2}$), where n_{2} is the lens refractive index, n_{1} is the surrounding medium, $R_{1}$ is the radius of the first surface the light hits, and $R_{2}$ is the radius of the second surface.

Important: A convex lens (converging in air) can become diverging if placed in a medium with refractive index greater than the lens material. For example, a glass lens (n=1.5) in carbon disulfide (n=1.62) acts as a diverging lens.