Requirements for Ideal Image Formation
Aberration represents a deviation of an actual image formed through an optical system from ideal image formation.
The requirements for aberration-free image formation, i.e. ideal image formation must meet the following three points.
(i) All light beams emitted from a certain point and passing through the image-forming optical system converge to a point.
(ii) The image points corresponding to individual object points that are coplanar on a plane perpendicular to the optical axis exist on a same plane.
(iii) An object planar shape and an image planar shape which are coplanar on a plane perpendicular to the optical axis are kept in a scaling relationship with each other.
In an actual optical system, however, it is very difficult to strictly meet the ideal image-forming requirements, thus causing an aberration that degrades the image-forming performance.
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