Chromatic Aberration What and Why ?
Courtesy of Mastin Labs
WHAT IS CHROMATIC ABERRATION?
Chromatic aberration is a very common problem in lenses, and is sometimes referred to as “color fringing” or “purple fringing”. Chromatic aberration can present itself as blurring or coloring of red, green, blue, yellow, purple, or magenta around the edges of an image. These colors are especially likely to appear in high-contrast photos with extreme highlights and shadows.
Chromatic aberration occurs because the lens of your camera is virtually a prism. As light passes through the prism, the light is bent and the color wavelengths become separated. Lens imperfections can cause the light to bend incorrectly, and certain wavelengths to change their speed or angle. This results in unsynchronized wavelengths and consequential color blurring and abnormalities in the image.
Virtually no lens is perfect and every lens suffers from chromatic aberration to some degree. It is such a common occurrence in photography that many DSLRs have in-camera post-processing technologies to help correct chromatic aberration as it happens. If your camera does not have this ability, if your lens is visibly displaying chromatic aberration, or if you simply want tips on how you can control chromatic aberration, read on for an overview on the two types of chromatic aberration and a few ways you can reduce or eliminate it; in camera, and in post processing.
CHROMATIC ABERRATION: TWO TYPES
Longitudinal (or axial) Chromatic Aberration
This type of chromatic aberration occurs when color wavelengths do not join at the same point after passing through a lens.
Signs: If your image has color fringing around objects throughout the image, even in the center, and if the colors that appear are red, green, blue, or a combination of all of them.
Remedies: Faster aperture lenses are typically more prone to longitudinal chromatic aberration than slower lenses, so stop down your aperture. This may reduce it or fix it completely. To compensate for light when you stop down, remember that you can slow your shutter speed, boost your ISO, or add a flash or other light source.
Lateral (Transverse) Chromatic Aberration
Light wavelengths (colors) are bent and pass through the lens at an angle, refocusing on different places along a focal plane.
Signs: The burring effect is most visible at the corners of a high contrasted image, not in the middle.
Remedies: This effect will not be affected by stopping down the lens aperture. To remove lateral chromatic aberration, you must correct it in a post-processing program, like Lightroom.
HOW TO FIX CHROMATIC ABERRATION
There are some things you can do as a photographer to reduce or eliminate chromatic aberration in camera to reduce your need for editing in post.
Avoid High Contrast Situations
Chromatic aberration is aggravated in high contrast situations where there are extreme shadows and highlights in the same image. High contrast situations include:
- Harsh outdoor lighting
- Images with a light-reflective surface (ocean, sky, or a white backdrop)
- Indoor lighting with a bright light source.
Avoid the Extremes of Your Zoom Lens
Zoom lenses can exhibit various degrees of chromatic aberration, especially at their most extreme short and long focal lengths. If your zoom lens is showing chromatic aberration, you can usually reduce it by zooming towards the middle of the focal range.
Fix It In Post
Whenever possible, try to fix chromatic aberration in-camera, fixing it in post is just more time added to your editing process. The good news is that if you absolutely have to save the fix for later, you can usually remove chromatic aberration effectively in post if the image was originally shot in RAW.
Here are step-by-step instructions on how you can fix chromatic aberration using Adobe Lightroom.
Chromatic aberration occurs so frequently in photography; but thankfully, these straightforward strategies for reducing, eliminating, and fixing chromatic aberration are simple. With the power to restore otherwise unusable images, knowing how to manage chromatic aberration is a valuable skill for every photographer.
HOW TO REMOVE CHROMATIC ABERRATIONS IN ADOBE LIGHTROOM
Step 1. Open Lightroom and zoom in on a part of your image where you see visible chromatic aberrations.
Step 2. Click to the ‘Lens Correction’ panel (in the ‘Develop’ module) in either the ‘Basic’ or ‘Color’ tab.
Step 3. Click the ‘Remove Chromatic Aberrations’ checkbox to turn it on.
After you’ve completed Steps 1-3, zoom out and look at your image. For most images, this simple process will do the trick to cure chromatic aberration in Lightroom, and you can move on to other editing.
If some chromatic aberration is still visible in your image after completing Steps 1-3 above, move on to Steps 4 and 5.
Step 4. Click on the ‘Color’ tab in the ‘Lens Correction’ panel.
Step 5. Observe the remaining color. If you still see a green line around the edges of your image, increase the ‘Amount’ slider above the ‘Green Hue’ option by sliding it to the right until the fringe disappears. Repeat this action for the ‘Purple Hue’ if you’re observing a purple fringe.