Q. There are two major types of aberration (defective image formation) in lenses: spherical and chromatic. Spherical aberration comes from fact that a spherical lens has the property of focusing parallel rays to a single point only approximately. This approximation is better the closer the rays are to the axis of the lens, but there would always be some improper focusing. Chromatic aberration comes from the fact that different wavelengths of light have different indices of refraction in a specific material, the property known as dispersion. This means that a lens has different focal lengths for different wavelengths of light. Consider a lens made to the following specifications: radii of curvature R_1 = 20.00 centimeters and R_2 = -20.00 centimeters, and refractive indices for red and blue light of n_{rm red} = 1.511 and n_{rm blue} = 1.530.

What is Delta f, the magnitude of difference in the lens's focal length between red and blue light?