# Geometric Optics¶

## Lens Formula¶

$$\large \frac{1}{\text{O}} + \frac{1}{\text{I}} = \frac{1}{\text{F}}$$

(+): Convergent

(-): Divergent

## Lensmaker's Equation¶

$$\large \frac{1}{f} = (n-1) \left( \frac{1}{R_1} - \frac{1}{R_2} \right)$$

where

$f$: focal length of the lens,

$n$: refractive index of the lens material,

$R_{1}$: radius of curvature (with sign, see below) of the lens surface closer to the light source,

$R_{2}$: radius of curvature of the lens surface farther from the light source.