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The Lens tab

The controls in the Lens tab let you address two problems, one common, the other pretty rare. If you use zoom lenses, you'll almost certainly run into chromatic aberration—color fringing along high-contrast edges caused by the inability of the lens to bring all the wavelengths of light to focus at the same plane—at some point in your work. Digital capture is extremely demanding on lenses, and it's not at all unusual for a lens that performs superbly on film to show some chromatic aberration on digital captures, particularly at the wide end of the range. Vignetting, where the corners are darkened because the lens fails to illuminate the sensor evenly, is rarer, but you may encounter it at very wide apertures. The controls in the Lens tab let you address both problems—see Figure 3-42.

  • Chromatic Aberration controls. Camera Raw offers two Chromatic Aberration sliders, one to address red/cyan fringing (Chromatic Aberration R/C), the other to address blue/yellow fringing (Chromatic Aberration B/Y). They work by adjusting the size of the red and blue channel, respectively, in relation to the green channel.

    The adjustments have remarkably little impact on the rest of the image. Mathematical comparisons of the non-edge pixels may reveal a one- or two-level difference in one channel in a few areas; but I've yet to see a difference that could be detected visually, so don't be afraid to use these controls to eliminate color fringes. Two tips may help you do so.


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