The focal length of a convex lens is

The focal length of a convex lens depends on the refractive index of the lens material, which varies with the wavelength (color) of light [t1][t3]. According to the Lens Maker's Formula, the focal length is inversely proportional to (n-1), where 'n' is the refractive index [t3][t6]. Based on Cauchy's equation, the refractive index is higher for shorter wavelengths [t6]. Since blue light has a shorter wavelength than red light, it experiences a higher refractive index and is refracted (bent) more sharply toward the optical axis [t1][t4]. Consequently, blue light converges at a point closer to the lens than red light [t1][t9]. This results in the focal length for blue light being shorter than the focal length for red light, a phenomenon that contributes to chromatic aberration in simple lenses [t1][t4].