Chromatic Aberration
Chromatic aberration is color fringing — usually green or purple — caused by a lens failing to focus every wavelength of light to exactly the same point on the sensor. It's most visible along high-contrast edges (a dark branch against a bright sky, for example) and typically most pronounced at a lens's widest aperture, growing harder to see as it's stopped down.
Apochromatic (APO) lens designs correct this aberration across a wider range of the color spectrum than a standard achromatic design, producing noticeably cleaner, higher-contrast results in demanding high-contrast scenes — a specific engineering focus that becomes progressively harder to achieve as focal length increases and maximum aperture widens, which is why apochromatic correction is most often marketed on fast telephoto primes specifically.
Frequently Asked Questions
Can chromatic aberration be corrected after the fact?
Yes, largely — most photo-editing software includes automatic or lens-profile-based chromatic aberration correction that removes most of the visible fringing, though a genuinely well-corrected lens still produces cleaner results before any software correction is applied.
Is chromatic aberration the same as purple fringing?
Purple fringing is a common visible symptom of chromatic aberration, particularly around backlit high-contrast edges, though not every instance of chromatic aberration appears specifically as purple — green fringing is equally common depending on the specific optical cause.