2015 Volume 36 Issue 3 Pages 40-44
Deviations from an ideal image are called aberrations. An ideal optical image satisfies the following three conditions. 1) A point object creates a point image. 2) A plane object perpendicular to the optical axis creates a plane image. 3) A figure on a plane perpendicular to the optical axis creates an image similar to itself. There are two kinds of aberration: monochromatic aberrations and chromatic aberrations. Spherical aberration, coma, and astigmatism cause images to be blurred. Field curvature and distortion deform the image of a figure. These are referred to as Seidel aberrations and monochromatic aberrations. Chromatic aberrations are the result of the refractive index of a medium being a function of the wavelength. There are two kinds of chromatic aberration: longitudinal chromatic aberrations and lateral chromatic aberrations. The sine condition is not an aberration but rather is a very important requirement for correction of coma by a lens. It is expressed as follows: β=n1sin u1/(n2sin u2), where β is lateral magnification and n1,u1 and n2,u2 are the index and slope angle of a ray in object and image space, respectively.
