Chromatic aberration is a phenomenon caused by distortion of the lens. Basically, it is a failure of the lens to focus all the colors to the same convergence point.
The effect can be generally seen in dark edges adjacent to bright areas of an image; it looks like an out-of-focus ghost of magenta or purple color. In photography this is also called “purple fringing”.
The quality of the optic plays an important role here, as not all lenses will produce the same effect. This problem tends to manifest much more in zoom lenses with variable aperture. However, no lens is exempt from having some distortion……
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