Chromatic aberration is an inherent problem in the manufacture of lenses. It is the failure of the glass to bend the light in such a way that it focuses all the colors at the same point, and it occurs because lenses have a different refractive index for different wavelengths of light. It is characterized by color fringing, or unwanted colors at the edge of objects. The colors can be red, cyan, green, magenta, blue, or yellow. You usually can’t see this fringing until you magnify the image quite a bit, but at 100 percent and higher it’s quite obvious. I’ve enlarged (#1) to 300 percent, and in (#2) you can see what I’m talking about. Chromatic aberration is quite pronounced in wide angle lenses, and it’s most obvious in the corners. The picture of this famous pool in the Gellert Hotel, Budapest, Hungary was taken with a 14mm lens. The center of the lens is largely devoid of these unwanted colors. Telephotos also have chromatic aberration, but it is usually not as bad.
#1 (Left) #2 (Right)
All Photos © Jim Zuckerman, All Rights Reserved
There is a command in Photoshop that addresses this issue—Filter>Distort>Lens Correction—but it doesn’t do a good job at eliminating the undesirable color. A much better option is to use the Lens Correction option in Adobe Camera Raw (this is another reason for shooting in Raw mode). When you open ACR, there is a small icon that says “Lens Correction” when the cursor is moved over it (figure A). When you click on this, a dialog box opens and the two slider bars at the top under Chromatic Aberration control the elimination of the color. You will need to magnify the image in the large thumbnail area so you can see clearly when the color fringing is gone, but this is a fantastic tool to solve a problem that has plagued photographers (and lens manufacturers) for a very long time.