Camera lenses can exhibit different types of defects at certain focal lengths, f-stops, and focus distances. You can correct for these apparent lens distortions using the Lens Corrections panel of the Develop module.
Vignetting causes the edges of an image, especially the corners, to be darker than the center. It is particularly noticeable when the photo contains a subject that is supposed to be an even shade or tone, such as the sky in a landscape image.
Barrel distortion causes straight lines to appear to bow outward.
Pincushion distortion causes straight lines to appear to bend inward.
Chromatic aberration Chromatic aberration appears as a color fringe along the edges of objects. It is caused by the failure of the lens to focus different colors to the same spot, aberrations in sensor microlenses, and by flare. Lightroom provides a checkbox to automatically correct blue-yellow and red-green fringes, also known as lateral chromatic aberration.
Lightroom 4.1 and later provides slider controls to correct purple/magenta and green aberration (axial chromatic aberration). Axial chromatic aberration often occurs in images made with large apertures.