Axial chromatic aberration

Chromatic aberration (color fringing) comes in two types. Lateral chromatic aberration is the most obvious sort, showing up as sharp color fringes around object outlines, which are easy to remove digitally. Axial chromatic aberration is less obvious and very difficult to fix digitally. It shows up as bigger, softly rendered color fringes around out of focus objects.

Axial chromatic aberration is a particular problem for portrait or event photographers who rely on defocused backgrounds and foregrounds as part of their signature creative style.