Correcting Lens Errors
Unfortunately, Photographic lenses are seldom perfect. They produce some optical errors due to refraction caused by different wavelengths of light, different types of glass, lens construction issues, and other factors. Lens errors are stronger in some lenses and weaker in others, and often depend on the focal length and aperture of the lens being used. Zoom lenses especially represent a compromise between versatility and optical quality, with the most obvious errors occurring at large apertures and at the extreme ends of the zoom scale. The three most common types of lens error are:
Wide-angle lenses (with equivalent focal lengths of 35mm and less) are particularly susceptible to barrel or pincushion distortion. ...