When shooting "wide" you will often encounter the "barrel" effect which exhibits itself with the edges of your image curling up in a bowl shape. The other extreme is the "pin cushion". This distortion causes the center of your image to bulge out/up in a pin cushion shape. The good news is that the new Lens Correction Panel in Adobe Lightroom 3 can make quick work of these types of distortion.
In most cases, the only action required on your part is to select the "Enable Profile Corrections" box on the Lens Correction Panel. Lightroom reads the metadata from your image to determine the camera and lens models and then applies its own preset to iron out the anticipated distortion effects. If after applying the preset, you think the correction missed the mark, you can further adjust for distortion using the Distortion slider. Clicking on the slider provides a grid overlay on your image. To pull the center of your image down (reduce pin cushion), drag the slider to the right. To push the center of your image up (reduce barrel distortion), drag to the left while reviewing the results beneath the grid overlay.
The "C. Aberration" slider helps you deal with Chromatic Aberrations or those blue or red halos that appear around the edges of objects in your image. Again, the "Enable Profile Corrections" will apply a correction based on the camera/lens model but you can apply greater control by manipulating the slider. We'll go into more detail next week when we review the "Manual" method of Lens Correction.
The last slider helps you to address Vignetting. Have an image where the corners appear darker than the rest of the image? Simply drag the Vignetting slider to the right until the darkness disappears.
If you find you're always making the same corrections in the Lens Correction Panel, simply save your changes as a preset for reuse.
Next week we'll take a look at the "Manual" method which gives you full control to adjust for perspective anomalies, vignetting and chromatic aberrations.
Until next time, keep click'n.