Chromatic aberration is a common problem in photography. Sometimes called color fringing, it is a type of distortion that results in the addition of an artificial color around the edges of subjects in a photograph. It is especially visible in high contrast areas, such as a dark object against a light background.
How Chromatic Aberration Occurs
Due to the refractive nature of glass, each color, or wavelength of light, passes through the lens at different speeds. This causes each wavelength to bend at different angles and arrive at the focal plane at different positions. As a result, a camera lens does not focus the different colors of light onto the same focal plane.
Quality suffers. And if you plan to work professionally in photography, you need to know about this image anomaly and how to deal with it. In this article, we’ll help you understand chromatic aberration, why it occurs, tips on identifying it, and how to correct or minimize it.
Minimizing Chromatic aberration
Lens manufacturers allocate significant resources to chromatic aberration correction. It is a complex form of distortion. Camera and lens makers devise very specific techniques to minimize it, employing in-camera software and post processing programs. The goal is to reach a circle of least confusion, where all the wavelengths arrive at the same point on the focal plane. This is where chromatic aberration is at its minimum.
In Search of the Perfect Lens
When light rays pass through a lens, the different wavelengths, or colors, disperse. So each color travels at its own angle, according to the refractive index of each lens element. A perfect lens would direct the various wavelengths to arrive at the same plane – the camera’s focal point – in unison, as in the diagram below.
But lenses are not perfect. Constructed of multiple glass elements, each one contributes to the angle at which the wavelengths travel. Zoom lenses bring further complications as those glass elements are constantly rearranging inside the lens housing.
And the job of a lens is not merely to deal with purple fringing. We also call on lenses to deliver sharp images with true color rendition and a minimum of distortion.
What are the Types of Chromatic Aberration?
Two types of chromatic aberration are common in photography.
Lateral or Transverse
This is blue-yellow, red-green, or purple fringing, primarily near the edges of the frame. It frequently appears in photos taken with short focal length lenses. This anomaly can be corrected in post-processing. However, it may result in a loss of sharpness.
Axial or Longitudinal
This is a color fringing most pronounced in the middle of the frame, especially at high-contrast edges. This is also called focus shift. It frequently affects images taken with long focal length lenses.
It appears as a blurry purple or green color fringing around the subject in focus. Axial aberration can also be removed or minimized in the image processing software.
One or Both May be Present in Images
Although these two types of chromatic aberration have different criteria, both may occur in the same image.
Longitudinal chromatic aberration happens across the entire image. Decrease it by shooting at a smaller aperture. This brings a greater depth of field. So even though the different wavelengths come into focus at slightly different distances, the overall focus is good.
Lateral chromatic aberration is least visible at the photo’s center; however, it increases toward the edge of the frame. And decreasing the aperture has little or no effect.
Avoid Color Fringing in the Camera
Photographers have methods to deal with this optical issue in-camera. A high quality lens is a good place to start. Apochromatic lenses and low-dispersion lens elements reduce chromatic aberration. In addition, the achromatic lens is a combination of elements with the same focal point for red and blue light, mostly eliminating the effects of wavelength dispersion.
Avoid cheap lenses, some of the older lenses, and low quality teleconverters. That reduces the chromatic aberrations that you would have to cope with in post production.
In addition, some of the newer cameras contain built-in lens correction to mitigate transverse aberration; however, a certain amount is unavoidable.
PhotographyCourse offers many articles on lenses to help you select what’s best for your specialty.
Shooting Techniques to Reduce Chromatic Aberrations
Shooting high contrast subjects is almost certain to produce chromatic aberration. This is especially troublesome with dark subjects against a light background. Avoiding these settings entirely is not practical, but many photographers take steps to manage the issue.
Color fringing is most visible in images taken at wide apertures. An image shot at f-1.8 is more likely to exhibit some chromatic aberration. So shooting at a mid-range of f-5.6 or f-8 takes advantage of the lens characteristics and minimizes the color fringing. To compensate for the smaller aperture, increase the ISO or shoot at a slower shutter speed.
In addition, wide-angle lenses tend to produce chromatic aberration. The short focal lengths mean you’re using the extremes of the lens elements. For example, with a 24-70 mm zoom lens, shooting at a focal length of around 50 mm should eliminate or reduce chromatic aberration.
How to Correct Chromatic Aberration in Post Processing
Before we get into dealing with aberrations after the shoot, I’d like to point out this: the best method of producing stunning photos is to get it right in the camera. I prefer doing less in terms of correcting defects of lens dispersion or other issues in post production. The more I get done in camera and the less I have to deal with in processing, the better.
However, as photographers we have a number of excellent options for adjusting images after the shoot. Adobe Photoshop and Adobe Lightroom are industry leaders. And you can choose either automatic correction or manual. Both are highly effective.
The Lens Corrections Module in Lightroom
Lightroom’s Lens Corrections module reduces or in some cases erases the blurred colors of chromatic aberration. The photo below shows the module in Profile mode. This automatically removes chromatic aberration and other issues according to the lens profile built into the software.
The photo below shows the Lens Corrections module in manual mode. In this configuration, you can adjust the defringe amount and fine-tune the hue of both the purple and green fringes. Or you may opt to sample the fringe color with the eyedropper tool to get a more precise setting of the hue, then make the adjustments to defringe.
The Optics Module in Photoshop
Chromatic aberration can be corrected in Photoshop, as well, using the Optics module in Camera Raw. Essentially, Photoshop borrowed the Lightroom module.
You can use Defringe sliders to adjust the hue and the amount of purple and green fringing. You also have to option to sample the fringe using the eyedropper tool, as shown in the photo below.
In addition, the Lens Correction Filter in Photoshop offers a choice of Auto Correction or Manual adjustments. Combine this with Gaussian Blur, Blending Modes, and Masking, and you can achieve quality outcomes.
Other Options for Removing Chromatic Aberration
Adobe Photoshop and its photo processing partner, Adobe Lightroom, are well known. But you might want to explore alternatives.
Nikon offers a feature to reduce lateral chromatic aberration in its Capture NX2 application.
Get Creative with It
While most photographers work to eliminate it, chromatic aberration finds some creative uses. The TikTok logo comes to mind.
Photographers and graphic designers have experimented with the effect. It ranges from artistic to headache-inducing.
Intentional chromatic aberration can be achieved in a number of photo processing programs. These programs split the red, green, and blue channels, creating an image with a red fringe visible on one side and green on the other.
The effect is similar to an old 3-D photo. It adds a sense of movement and a bit of a disorienting feel to the image.
Until lenses are perfected, chromatic aberration remains a fact of life in photography. We’ve outlined several techniques for reducing this distortion to an acceptable level.
You can take steps to use your knowledge of light and the characteristics of the lens to your advantage to minimize this distortion as you shoot. Then you can further reduce it in post processing.
Understanding chromatic aberration, how to work around it, and how to minimize it takes another step in developing your skillset as a photographer.