I. What is Chromatic Aberration
Chromatic Aberration (CA) refers to the phenomenon where a lens fails to focus all wavelengths of light to the same focal point, resulting in colored fringes (commonly purple, green, or red) along high-contrast edges. Its essence lies in the dispersion of optical materials—the refractive index n varies with wavelength λ (e.g., shorter wavelengths have a higher refractive index)—causing different colors in white light to follow different paths and focus at different positions, thus inducing this type of aberration. Chromatic aberration is an inherent characteristic of optical systems (determined by the refractive index of materials and lens design) and cannot be completely eliminated. However, it can be suppressed to a certain extent through hardware optimization or software algorithms.

II. Two Types of Chromatic Aberration:

Longitudinal (Axial) Chromatic Aberration
Refers to the shift in focal positions of different wavelengths along the optical axis, leading to overall or local blurring and false colors in the image. It is more pronounced in large-aperture lenses and can be mitigated by stopping down the aperture, but not entirely eradicated.
The specific manifestations are shown in the figure below:

Lateral (Transverse) Chromatic Aberration
Refers to the directional color fringing that appears only at the edges of the frame or in high-contrast areas, caused by the variation in image magnification with different wavelengths.
The specific manifestations are shown in the figure below:
Unlike longitudinal chromatic aberration, lateral chromatic aberration never appears at the center of the image and only occurs in high-contrast areas. Blue and purple fringing at the edges is relatively common in some fisheye, wide-angle, and low-quality lenses. Lateral chromatic aberration cannot be eliminated by the lens itself, but it can be reduced in post-processing software.