When different colors of light
propagate at different speeds in a medium,
the refractive index is wavelength dependent. This phenomenon is known
as dispersion.
A well-known example is the glass prism that disperses an incident beam
of
white light into a rainbow of colors . Photographic lenses comprise
various
dispersive, dielectric glasses. These glasses do not refract all
constituent
colors of incident light at equal angles, and great efforts may be
required to
design an overall well-corrected lens that brings all colors together
in the
same focus. Chromatic aberrations (CA) are those departures from
perfect
imaging which are due to dispersion. Where the Seidel aberrations are
monochromatic, i.e. they occur also with light of a single color,
chromatic
aberrations only make their appearance in polychromatic light.
Color fringing is caused by lateral chromatic
aberration, one of the two types of chromatic aberration in lenses,
both of which arise from dispersion in glass. color
fringing, which appears as magenta and green bands at contrast
boundaries. Color fringing increases with the distance from the center
of the image; it's worst at the corners.
