Chromatic aberration
Chromatische aberratie · Lens & optics
An optical defect where the lens fails to focus all colours of light at the same point, causing coloured fringing.
It shows up as purple or green fringing along high-contrast edges, such as a dark branch against a bright sky. Cheaper lenses and wide apertures make it worse. In Lightroom and Camera Raw, chromatic aberration can be removed with one click via the lens correction options.
Tools that help with this: