Chromatic aberration

Chromatic aberration in photography is a result of the lens failing to focus all colors to one convergence point in a proper manner. This phenomena is evident as color fringes, especially visible along edges that separate highly contrasting areas such as dark and bright parts of an image.

Every color in the optical spectrum has a different wavelength. When the lens fails to focus all those varying wavelengths to the same convergence point, the result is what we know as chromatic aberration (also known as CA, achromatism, or chromatic distortion).

Types of Chromatic aberration

There are two types of chromatic aberration: Longitudinal or Axial chromatic aberration, and Lateral or Transverse chromatic aberration. Longitudinal chromatic aberration occurs when the lens fails to focus different wavelengths of light to the exact same focal plane, so different wavelengths are being focused at varying distances from the camera lens. Lateral chromatic aberration occurs when the lens fails to consistently magnify differing wavelengths equally. Both types of chromatic aberrations can occur concurrently in one photo, and the degree of chromatic aberration depends on the glass dispersion though is believed to be more visible with wide angle lenses.

Glass dispersion and chromatic aberration

We’ve all seen that photo of a glass prism that scatters a white beam of light into a rainbow of colors once passed through it, as shown on one of Pink Floyd album covers .

Photographic lenses are made of multiple glass elements. These glass elements have varying dispersive qualities, so they refract all constituent colors of incident light at different angles. Chromatic aberrations are those departures from the correct refraction angle due to lens dispersion.

Color fringing

Purple fringing is commonly seen in many digital photographs especially at areas where blooming occurs, though not all color fringing can be associated with chromatic aberration.

In digital photography, fringing may be attributed to the digital sensor only being able to preserve one or two color channels while blowing out the third due to varying sensitivity to different colors. Edges of highly contrasting areas suffer the most, especially if they’re being backlit.