pincushiondistortion

Pincushion distortion, sometimes simply called pincushion distortion, is a type of radial distortion observed in images produced by lenses. In this form of distortion the magnification increases with distance from the image center, causing straight lines to bow inward toward the center of the frame and the corners to appear pinched. It is the opposite of barrel distortion, where magnification decreases with radius and lines bow outward. Pincushion distortion is commonly associated with telephoto and certain zoom lenses and can be described mathematically by a positive radial distortion coefficient.

Causes and characteristics: Pincushion distortion arises from the optical design and projection geometry of the lens onto the sensor. It tends to be more pronounced in telephoto and some zoom configurations and increases toward the periphery of the image. The magnitude is typically represented by a positive radial distortion term in standard lens models, and it can vary with focal length, lens manufacture, and alignment.

Measurement and correction: Distortion is typically estimated through camera calibration using images of known patterns (such as checkerboards) to derive intrinsic parameters and distortion coefficients. Software tools, including lens correction modules and image processing libraries, apply undistortion maps to rectify the image. In professional workflows, distortion correction is performed per lens and focal length, often integrated into raw development pipelines or through dedicated calibration profiles.

Impact and notes: Pincushion distortion can affect architectural or technical photography where straight lines must be preserved. Mild distortion is common and may be acceptable in casual photography. Correcting pincushion distortion is routine in post-processing, and readers should distinguish it from barrel distortion, which requires a different correction direction.