Optical Systems lecture 4

Lecture 4
1-5 Distortion
In geometric optics, distortion is a deviation from rectilinear projection; a projection in which straight lines in a scene remain straight in an image. It is a form of optical aberration.
Although distortion can be irregular or follow many patterns, the most commonly encountered distortions are radially symmetric, or approximately so, arising from the symmetry of a lens. These radial distortions can usually be classified as either barrel distortions or pincushion distortions. In barrel distortion, image magnification decreases with distance from the optical axis. The apparent effect is that of an image which has been mapped around a sphere (or barrel), as shown in figure (1-5).

In pincushion distortion, image magnification increases with the distance from the optical axis. The visible effect is that lines that do not go through the centre of the image are bowed inwards, towards the centre of the image, like a pincushion, as shown in figure (1-5).
A mixture of both types, sometimes referred to as moustache distortion or complex distortion, is less common but not rare. It starts out as barrel distortion close to the image centre and gradually turns into pincushion distortion towards the image periphery, making horizontal lines in the top half of the frame look like a handlebar moustache, as show in figure (1-6).