16.4 Refraction at Curved Spherical Surfaces and Lens maker's FormulaClick here to enlargeO : Point object, OP = u = Object Distance P : Pole, C : centre of curvature, PC = R = Radius of curvature I : Point Image, PI = v = Image distance i, r, a, b, g are small enough for sin i ~ i ~ tan i to hold etc n! and n" refractive indices of rarer # denser media $%ith res&ect to vacuum or air as incidence medium' ( Note :$!' )he formula holds for concave refracting surfaces as %ell$"' )he formula holds even if the incidence medium is denser and the refracting medium is rarer ie n! * n"Lens aker's formulaClick here to enlargeInitiall+ medium of RI n" is assumed to e,tend to infinit+, then for refraction at surface I, %e have,%here v- is the distance P, I- of the intermediate image.o%, the medium of RI n" is cut off be+ond surface II, therefore the medium on the rightside is again of RI n! , the intermediate image I- %ill behave as if it is object for refraction at IInd surface, due to refraction at surface I the final image is formed at I$iv' /nlike mirrors %here f = r0", there is no uni1ue relation bet%een f and R of a lens( for, even if R! = R"ie bi2conve, or bi2concave lens