Chromatic aberration : The focal length of a lens is different for different colors, being more for the red color than for the violet color. When a ray of white light is incident on a lens, it is dispersed. As a result, different colours come to focus at different points on the principal axis. The image of a point object is not a point but is spread along the axis and is coloured. The failure of the lens to bring rays of different colors to focus at the same point is called chromatic aberration. It can be reduced by using a concave lens of suitable material and focal length.
