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Chromatic aberration is an optical phenomenon in which correct images cannot be produced due to the inability of the camera lens to focus the wide range of wavelengths of light on the same plane. In other words, the colors are wrongly refracted/bent by the camera lens, causing a mismatch at the focal point, as a result of which the colors do not combine as they should. This often results in a fringe or halo around objects. Chromatic aberration has uses, especially in ophthalmology, where it is used in the duochrome eye test to assure the correct power of lens is being used by the patient.
Chromatic aberration is also known as chromatic distortion, spherochromatism, color fringing or purple fringing.
In high-contrast scenes and while shooting at wide apertures, chromatic aberrations usually flare up. Chromatic aberration is more or less controlled in the center of the frame. However it is not the same when it comes to image corners. Dispersion of the glass used determines the amount of chromatic aberration. There are two main categories of chromatic aberration, namely axial chromatic aberration and lateral chromatic aberration. When different wavelengths of light are focused from the lens at different distances, axial aberration happens. Lateral aberration occurs due to different wavelengths being focused at different positions in the focal plane. In addition to color photography, chromatic aberration can also impact black and white photography, in which chromatic aberration causes images to be blurred.
When shooting in RAW, chromatic aberration can be effectively eliminated in post processing. In order to correct chromatic aberration, lens makers often make use of achromatic lens design. In this design, a second lens that has a different dispersion than the main lens is used to correct the chromatic aberrations that the ray of light suffers while passing through the first lens. Certain third-party tools are also capable of minimizing chromatic aberration. In the case of black and white photography, chromatic aberration is minimized with the help of a narrow-band color filter.