Chromatic aberration
CHROMATIC ABERRATION The focal length of a lens depends on the refractive index of the substance to form and the geometry of surfaces. Since the refractive index of all substances varies with optical wavelength , the focal length of a lens is different for different colors . Consequently, a single lens is not simply an image of an object, but a series of images at different distances from the lens, one for each color present in the incident light. Furthermore, since the increase depends on the focal length, these images are different sizes. The variation in image distance with the index of refraction is called longitudinal chromatic aberration and the variation in size of the image is the lateral chromatic aberration . The light of wavelength shorter (blue) is bent more than light of longer wavelength (red), so that blue light reaches a focus closer to the lens than red light. The effect can be reduced by placing two lenses together. Mirrors do not suffer from chromatic aberra...