The other day I was working on an image and having a terrible time getting the sharpness and color that I wanted. Upon closer inspection, I noticed that the image suffered from some pretty serious chromatic aberration.
What is Chromatic Aberration
When white light passes through a prism, a rainbow of colors is produced. This phenomenon occurs because of the prism’s index of refraction varies depending on the wavelength of the light.
Remember, white light contains a uniform mix of a full spectrum of colors. And each color of light has a different wavelength. Simply stated, each color wave bends at a different rate.
Photographic lenses are essentially fancy prisms bending light to focus an image on a single plane. Camera manufacturers have been wrestling with the problem of chromatic aberration for years. But they’ve made some incredible technological advances. Even so, it is not something which they’ve been able to eliminate totally.
There are two types of chromatic aberration. The first is called axial chromatic aberration. This is where the focal point varies according to the wavelength. In such cases, there appears a color blur or flash.
The second is chromatic difference of magnification. This is where the image magnification in peripheral areas varies according to the wavelength. This shows up in photographs as color fringing - usually along borders between high contrast elements. This is what you see in the example above.
How do You Eliminate Chromatic Aberration?
First, it’s pretty safe to say that you can’t totally eliminate chromatic aberration. Manufacturers have made great strides in minimizing its effects. Lenses today have special coatings and the materials used in the optics have helped. You also find a manufacturing technique called Diffractive Optics which uses tiny lattices on the lenses. Just remember that each of these improvements adds to the cost of a lens. It’s this reason that some of the better optics carry the price tags they do. Yes, there really is a benefit to pay for the better optics.
Something else that is very helpful are the post processing capabilities of programs like Adobe Lightroom. In the Lens Corrections tab in the Develop module, you’ll find two magical options; Enable Profile Corrections, and Remove Chromatic Aberration. The options use the metadata to identify your specific lens and then apply corrections customized to your camera. And it works pretty well.
Our good friend Julianne Kost has a blog entry that shows how to use this. Check out her February 12, 2016 blog entry for details.