Beams of white light strike a convex (converging) lens and cross (are brought to a focus). Higher frequency (shorter wavelength) colours, like violet, are refracted more. This dispersion of white light creates a fanning out of the colours of the rainbow (red, organ, yellow, green, blue, indigo, and violet, ROYGBIV). This is unwanted in optical instruments and is called chromatic aberration. It can be corrected by combining lenses with different powers of dispersion. The simulation uses the refractive indices of flint glass, a very heavy material with a high refractive index and high dispersion.