An optical doublet is formed from two lenses A, B made of glass of different refractive indices nA,ng. Lens A has two convex sides of radius of curvature R, and lens B has one flat side and one concave side of radius of curvature R. Derive an expression for the power of the doublet. Both refractive indices vary slightly with wavelength as follows: na = 1.50, 1.51, 1.52 at red, yellow, and blue respectively, while ng = 1.60, 1.62, 1.64 at the same wavelengths. Show that the doublet has constant power at all three wavelengths.

An optical doublet is formed from two lenses A, B made of glass of different refractive indices nA,ng. Lens A has two convex sides of radius of curvature R, and lens B has one flat side and one concave side of radius of curvature R. Derive an expression for the power of the doublet. Both refractive indices vary slightly with wavelength as follows: na = 1.50, 1.51, 1.52 at red, yellow, and blue respectively, while ng = 1.60, 1.62, 1.64 at the same wavelengths. Show that the doublet has constant power at all three wavelengths.