Barrel Distortion
A geometric distortion in which straight lines bow outward from the centre, as if the image were wrapped around a barrel.
Measured in
%
In depth
Barrel distortion is characteristic of wide-angle lenses and the short end of most zooms, and it is caused by magnification falling off toward the frame edges. It is purely geometric, so lens-profile correction removes it almost completely at the cost of a small crop. It only becomes objectionable when straight lines run near the frame edge.
Examples in practice
A doorframe photographed at 18 mm bows outward until a lens profile is applied in raw processing.