Thin Lens

A thin lens is formed by a transparent material bounded between two spherical surfaces, or between one spherical and one plane surface, with the separation between the two surfaces small enough to be neglected (hence 'thin'). Two spherical surfaces give two centres of curvature $C_1,C_2$ and two radii of curvature $R_1,R_2$; a plane surface is the limiting case of a spherical surface whose centre of curvature is at infinity and whose radius $R=\infty$. Nearly all of the vocabulary already developed for spherical mirrors -- pole, focus, sign convention for distances and heights -- carries over unchanged to thin lenses, with one key exception: the sign convention for the focal length …