Definition of the Fourier Plane

Please don’t allow the concept of the Fourier transform to intimidate you! The “Fourier” plane is simply the focal plane of a converging  optical lens such as the lens of the eye. This is the plane that most of us as children used with a magnifying glass to image the sun and burn holes in leaves, paper,etc. If this puts one off as thinking that the eye would never be like that consider that the pupil of the eye limits the amount of light allowed to enter the eye and that we never look directly into a bright source such as the sun.In the Fourier equation information  about the image is encoded at this plane in two terms (instead of one if the eye were the analogue of a camera)  light amplitude (related to intensity) and phase. Lying behind the Fourier plane is the “image plane” used by cameras and other imaging devices to form an image. These images are formed using only light amplitude and not phase information. The eye therefore possesses a superior ability to utilize phase detection in it’s image-forming process!