How is chromatic aberration in photography formed
What is chromatic aberration?
Chromatic Aberration, also known as color aberration, is a common optical problem, due to different wavelengths of light so that the lens can not gather all wavelengths of color to the same focal plane, or when the wavelengths of color gathered to a different focal plane position and the formation of chromatic aberration.
The wavelength of visible light for the average person is between 400nm (violet) and 700nm (red). The refractive index of a material (optical glass) varies with the wavelength of the passing light wave, and is called “dispersion”. The famous “trigonometry” experiment proves the existence of dispersion. Chromatic aberration is caused by the phenomenon of lens scattering, due to the difference in wavelength of different colors of light will be under the photographic lens, the image of the object around the high contrast may appear blurred or obvious color fringes (red, green, blue, yellow, purple, magenta) is called chromatic aberration.
A perfect view of the lens can focus all wavelengths to the same point, where the best focus and the smallest blur circle are as shown in the figure:
In fact, each wavelength has a different refractive index on the lens, which leads to two types of chromatic aberrations – longitudinal chromatic aberration and transverse chromatic aberration.
Longitudinal Chromatic Aberration
Longitudinal Chromatic Aberration (LCA), also known as “LoCA”, is formed when different wavelengths of color light do not converge at the same point after passing through the lens. A longitudinal chromatic aberration image will show red, green, blue or a combination of these colors at the edge of the object. Longitudinal chromatic aberration can be significantly reduced by reducing the lens aperture. A strong light fast lens is more likely to have longitudinal chromatic aberration than a slow small aperture slow lens.
A green color difference appears in the upper part of the figure, and a purple color difference appears in the lower part closer to the camera.
Lateral Chromatic Aberration
Lateral Chromatic Aberration (LCA) differs from vertical chromatic aberration in that it does not appear in the middle of the image, but only in high-contrast areas at the edges of the image. Blue and purple are often found in fisheye, wide angle and low quality lenses. Horizontal chromatic aberration cannot be eliminated by reducing the aperture, but it can be eliminated by post-production.
The camera uses visible light for imaging. When the light molecules of various visible light reaches the camera’s CCD (light-sensitive device), through electronics, the image is presented. When the intensity of light is good, the camera imaging is also good, but, with the light illumination (intensity) of the weakening, imaging also becomes worse, mainly in the “noise” to increase the appearance of the image also becomes blurred (such as changes in the camera image at dusk). As the light illumination is further reduced, the color camera can not be imaged.
In addition to the traditional definition of chromatic aberration, the commonly mentioned chromatic aberration in daily life refers to the meaning of color difference. The factors that cause chromatic aberration are not only wavelengths, but also different light sources, different lenses, photographic elements and display devices that can impress the color of images and form chromatic aberration.
Source: China colorimeter manufacturer