Menu: Adjust -> Chromatic Aberration
A simple lens will not focus different colors in the exactly same place because the refraction depends on the wavelength. Short (blue) wavelengths are refracted more than long (red) wavelengths. Camera lenses are made to correct or minimize the impact of aberration. Lens may be corrected for two primary colors (achromatic lens) or even for three primary colors (apochromatic). Camera lenses are very complex “masterpieces.” A very good lens will show just very little if any aberration defects. However, poorly a designed lens will suffer from aberration a lot.
The lens is more affected by aberration usually in tele mode with the aperture wide open. Especially large zoom lenses will suffer from this because it is virtually impossible to make corrected lenses for all zoom values.
Digital cameras suffer more from aberration than film cameras because of the large density of pixels in CCD - the uncorrected light can propagate to dark neighbors making the aberration more visible in high contrast images.
So the best chance to catch chromatic aberration with your digital camera lens is to look at images with high luminance contrast such as looking through tree on front of a bright sky etc.
The color of the aberration varies from blue to purple.
The Chromatic Aberration Removal tries to fix the aberration problems.
If the image suffers just a little from the aberration, it is probably safer to leave it as it is unless you like the color effect of the result.
The tool helps you to remove aberration of blue to red spectrums. With the red rectangle move the preview to a corner where it shows aberration.
The Orb will help you to visually correct (shift) the channels to minimize the aberration error. When moving it horizontally blue type of aberration will be affected, when moving vertically red/violet type of aberration will be affected. The Orb makes possible to "mix" the type of aberration and the strength/direction all with one control.
The human eye is also a simple lens and as such it theoretically must suffer from chromatic aberration as well. However, we don’t see such problems partially because our brain seems to filter any unwanted “data” and also a yellow pigment in the fovea helps to correct this problem by absorbing blue light.