Camera Basics #22 - What are chromatic aberrations?

Longitudinal / axial chromatic aberration (color longitudinal error), this imaging error occurs when the individual light colors hit the sensor differently, namely in front of or behind the sensor. This error can be reduced by stopping down. This effect also essentially ensures that the images appear blurred, because if the rays of light do not hit a point in a bundle, but rather in front of and behind it, this results in a soft focus or distortion of the image.

What do chromatic aberrations look like in images?

Where do chromatic aberrations occur?

Chromatic aberrations can be found everywhere, particularly on high-contrast edges and strong reflections such as bare metal and white edges. Image stabilization, whether on the lens or sensor side, can also lead to colour distortion in the form of chromatic aberration. Autofocus can also have the effect of increasing chromatic aberration, causing the distances within a lens to change and the light waves to be refracted differently.

Which focal lengths are particularly susceptible?

Now that we have talked about the physics, this question could be answered somewhat automatically, but chromatic aberration occurs due to the angle of refraction, as wide-angle lenses have a very large spherical lens and the curvature of the glass is very high in fisheye lenses, very strong aberrations usually occur here.

How to avoid chromatic aberrations?

You can reduce chromatic aberrations in the camera by closing the aperture. If you wanted to be really precise, you could turn off all peripheral factors: Stabilization and autofocus, as these elements have a dynamic effect on image quality. Reduce the strong contrasts, such as a burnt-out sky or other objects in front of a white wall/surface. What you can do here is reposition the light source or object to change the way the light falls and the angle at which it is reflected.

You can also work with a flash to influence the contrasts here, but don't forget that necklaces, earrings etc. still reflect and can lead to strong highlights.
If you want to reduce the chromatic aberrations in a panorama, it is best to use several individual images and merge them in post-processing, so that the angle is always changed and chromatic aberration is less pronounced.

How do manufacturers prevent/reduce chromatic aberrations?

When developing lenses, the lens manufacturer selects different glass elements with different coatings and material mixtures, which ensure different dispersions. It also helps if the manufacturer installs different glass elements that correct the curvature and bring the light rays back together a little more. This is called an achromat.

Removing chromatic aberrations in post-processing

RAW development tools have dealt with these errors in the past and most of them can remove them quite effectively. However, this often results in a gray edge because the color fringe is desaturated. Capture One, Adobe Lightroom, Luminar NEO and others all offer functions to reduce this error.

Conclusion

We have tried to explain the complexity of chromatic aberrations and how this problem arises. This unsightly distortion is a problem especially in inexpensive or less elaborately processed lenses and we hope that we have been able to clarify the price of some more expensive lenses.