What optical phenomena do the terms "pincushion" and "barrel" describe?

The terms "pincushion" and "barrel" describe types of distortion that can occur in optical systems, particularly in lenses. Pincushion distortion results in straight lines bowing inward towards the center of the image, resembling the shape of a pincushion. In contrast, barrel distortion causes straight lines to bow outward, creating a bulging effect similar to that of a barrel.

These distortions are typically found in wide-angle and telephoto lenses, where the geometry of the lens affects how light is projected onto the imaging sensor or film. Understanding these optical phenomena is crucial for photographers and optical engineers, as they can impact the accuracy and quality of the images produced. Recognizing and correcting for these types of distortions is an important part of image processing and lens design.