ABSTRACT
Lenses are used in optical systems such as binoculars, cameras, eyeglasses, microscopes, telescopes, and other optical systems. Coma derives its name from the pear-shaped comet-like appearance of the image of an off-axis point object located at a very large distance compared to the focal length of the lens. Assuming that the lens is free of spherical aberration, rays in the vicinity of the central ray form a sharp point image at A in the focal plane. Astigmatism is a monochromatic third-order aberration, which arises when a point object lies an appreciable distance from the optical axis of the lens. An optical system or a lens free of spherical aberration, coma, and astigmatism will provide a one-to-one correspondence between points on the object and image surfaces. In the absence of spherical aberration, coma, astigmatism, and field curvature, each point on a planar object would be sharply focused on a planar image plane.
