A definition of Chromatic Aberration
Chromatic aberrations form when different wavelengths of light come to focus at different points; this happens due to the refraction (bending) and dispersion (spreading) of light as it travels between two different mediums. Lateral, or transverse chromatic aberration is due to differences in magnification between different wavelengths, and is more visible towards the edges of an image. Its effects also increase with focal length. Axial, or longitudinal chromatic aberration results from different wavelengths of light coming to focus at different points on the optical axis. Lens manufacturers deal with chromatic aberration by combining elements with different properties, and through the use of special low-dispersion elements. Many cameras also attempt to remove chromatic aberration as part of their image processing.