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.