Chromatic abberation

In optics, chromatatic aberration (also abbreviated to CA) is a failure of a lens that occurs when light of different wavelengths or colors is refracted to different extents. This can lead to lateral chromatic aberration, which manifests itself primarily at image edges in green and red or blue and yellow color fringes at light-dark transitions. Longitudinal color errors can also occur in the form of different discolorations in front of and behind the focal plane.

apochromatic image of a building

Comparison of an image without and with chromatic aberration, in this case a lateral chromatic aberration.

Source: Wikimedia Commons (unchanged)
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Since such color errors should be avoided when digitizing, our systems work with a chromatic-corrected lens that compensates for this phenomenon. Otherwise, colored fragments would show around the edges of black letters, for example, and the scan would not be identical with the original.