Chromatic aberration is a phenomenon that occurs in optics when a lens fails to focus all colors to the same point, causing a color distortion that creates an outline of unwanted color along the edges of objects in a photograph. It is caused by dispersion, which means that the refractive index of the lens elements varies with the wavelength of light. There are two types of chromatic aberration: axial (longitudinal) and transverse (lateral) .

• Axial aberration occurs when different wavelengths of light are focused at different distances from the lens, causing focus shift. Longitudinal aberration is typical at long focal lengths.
• Transverse aberration occurs when different wavelengths are focused at different positions in the focal plane, because the magnification and/or distortion of the lens also varies with wavelength.

Axial chromatic aberration results in blurred colors in front of and behind the focus position due to the differences in each color’s focal point. It can be noticeable at the peripheries of extremely bright portions of an image. Lateral chromatic aberration, on the other hand, is the cause of color fringing and is only visible towards the corners of the image in high-contrast areas.

Chromatic aberration can be corrected in post-processing, but it results in permanent loss of some image detail. It can also be reduced by using smaller f/stops when taking photos. Chromatic aberration is used during a duochrome eye test to ensure that a correct lens power has been selected. Additionally, chromatic aberration can be added on purpose to videos or photos in Adobe Photoshop, Premiere Pro, or After Effects to create a unique look.