Have you ever heard the expression ‘the devil is in the details’? In photography, the devil is Chromatic Aberration (CA). In this article, you will learn how to deal with CA. First, by minimising it in-camera. Then, by correcting it in post-processing with Adobe Lightroom.
What Is Chromatic Aberration?Chromatic Aberration usually appears in the form of purple/red/blue/cyan/green fringes. They can be seen alongside high contrast edges. In laymen terms, CA means finding colors where they shouldn’t be. Every color behaves in its own particular way when passing through a material. A prism “disperses” them, and they form a familiar rainbow. The refractive index causes dispersion. This is the index of the material that light is passing through. Refraction is stronger for light of short wavelengths (blue). It’s less intense for light of long wavelengths (red). Different kinds of glasses cause refraction or dispersion of various intensities. There are two types of Chromatic Aberration: Longitudinal and Lateral Chromatic Aberration.
Longitudinal Chromatic Aberration
What Is Longitudinal Chromatic Aberration?Longitudinal Chromatic Aberration (LoCA) is also known as ‘axial’ aberration. It appears when the lens cannot focus on all the different colors on its focal plane (the sensor). One or more colors are then focused either in front of or behind the focal-plane.
What Does LoCA Look Like?LoCA appears in high contrast areas and is visible either at the edges or in the centre of the frame. It presents itself as a blurred purple or green fringe. It’s either in front or behind the object in focus. The image below shows some chromatic aberration. It’s along all the contrasting edges, regardless of their position in the frame. LoCA is easy to identify. It changes colours when you focus in front of or behind the object. And it disappears at a narrow aperture. Take a look at the image below. The blurred purple colour in the image taken at f/1.4 is in front of the window edge. It’s not only alongside it. This makes it difficult to correct in post-processing.
Transverse Chromatic Aberration
What Is Transverse Chromatic Aberration?Transverse Chromatic Aberration, TCA, is also known as lateral. It happens when the colors are on the focal plane, but not all in the same point. It is more present toward the edges of the frame and is not shown in the central part of the frame.
What Does Transverse Chromatic Aberration Look Like?Transverse Chromatic Aberration appears as sharp color fringing. It’s alongside high contrast edges of a dark or bright area. The color fringes are complementary colors along opposite edges. Left side green, right side red, and so on. Stepping down your lens does not correct TCA.
How To Reduce Chromatic Aberration on Your CameraThe lens industry puts great effort into minimising CA in their lenses. They do this with low dispersion optical glass and optical elements. Apochromatic lenses, for example, correct chromatic aberration. But a certain amount of both LoCA and TCA is unavoidable. High-quality lenses exhibit much less CA than:
- cheap lenses
- fast lenses when used wide open
- old legacy lenses
- cheap teleconverters and wide angle lens converters
- Avoid high contrast scenes
- Accurate focus to reduce the LoCA blur, making it look smaller
- Step down your lens by 1 stop or 2, i.e., by using smaller apertures, to remove LoCA
- Place your subject in the middle of the frame to make it TCA free and crop later to regain a better composition
- Expose for the highlights and avoiding blowing them up
- Avoid using the shortest and longest focal length on zoom lenses
- Experiment with different distances between you and the subject.