Lens Maker's Formula
An equation relating a thin lens's focal length to its material refractive index and the radii of curvature of its two spherical surfaces.
Governing formula
1/f = (n - 1) [ (1/R1) - (1/R2) ]
SI unit
m⁻¹ (Diopters)
In depth
Allows opticians to design spectacle and instrument lenses of exact desired focal power by grinding specific curvature radii $R_1$ and $R_2$.
Examples in the real world
Grinding a glass lens ($n=1.5$) with symmetric convex radii $R_1 = +20 cm$ and $R_2 = -20 cm$ to yield a $+20 cm$ focal length ($+5.0 D$).