The focal length of the lens varies directly with the wavelength of the light used and as wavelength is inversely related to refractive index, the focal length also varies inversely with it. This is the principal cause of the phenomena of chromatic aberration. The frequency of light has no effect on the focal length.So focal length increases with wavelength but decreases with refractive index and vice versa.And as focal length and power are inversely proportional.Therefore the power, focal length and chromatic aberration of a lens depend on the wavelength or wavelengths of incident light.