An optical engineer is designing an achromatic lens for a new microscope. The engineer combines two lenses of different materials and shapes (plano-concave and bi-convex), as shown in the image below. As a result, all the wavelengths of light will focus at the same distance, resulting in a sharper image. The engineer starts by selecting two materials for her lenses. The plano-concave lens has refractive indices n 1,b and n 1,r for blue and red wavelengths, respectively. The bi-convex lens has refractive indices n2,b, and n2,r for blue and red wavelengths, respectively. The curved side of the plano-concave lens and the curved side of the bi-convex lens have an equal radius of curvature, R. Determine the relation between n 2,b - n2,r, and n1,b -n1,r in order that the different wavelengths focus on the same point and eliminate chromatic aberration.