Skip to main content Accessibility help
×
Home
  • Print publication year: 2008
  • Online publication date: July 2010

11 - Aberrations in optical systems

Summary

Our tour through paraxial optics has only considered perfect images of scenes in which a point source in object space was mapped to a point in image space using paraxial rays. Gaussian optics also produced perfect images outside the paraxial region. Paraxial optics, however, is only a first-order approximation to a real optical system. Realizable optical systems do not produce perfect point images from point sources (represented mathematically as a delta function). In real optical systems, there is some blur or spreading of the point image.

Diffraction

The complex propagation of light passing through an aperture stop of a lens system will form a less than perfect image (for a detailed explanation of Huygens' wavefronts and propagation see Mahajan (2001)). In fact, the best one can do is to make the system “diffraction-limited.” Diffraction occurs when a wavefront (radiant beam) impinges upon the edge of an opaque screen or aperture. Light appears outside the perfect geometrical shadow because the light has been diffracted by the edge of the aperture. The effect this has on our simple rotationally symmetric optical systems is that a point does not map to a point, but is blurred or smeared. You may have observed the effect of the diffraction of light from a portal where there is light beyond what would be defined as the geometrical shadow boundary. If a wavefront, as shown in Figure 11.1, passes through a circular aperture, it does not continue as a circular disc.

Bibliography
Born, M. and Wolf, E. (1959). Principles of Optics, sixth edn. Cambridge: Cambridge University Press.
Hecht, E. (1998). Optics, third edn. Reading, MA: Addison-Wesley.
Jenkins, F. A. and White, H. E. (1976). Fundamentals of Optics, fourth edn. New York: McGraw-Hill.
Shannon, R. R. and Wyant, J. C. (1965). Applied Optics and Optical Engineering, Vol. III. New York: Academic Press.
Kingslake, R. (1978). Lens Design Fundamentals, New York: Academic Press.
Ray, S. F. (2002). Applied Photographic Optics, third edn. Oxford: Focal Press.
Smith, W. J. (2000). Modern Optical Engineering, third edn. New York: McGraw-Hill.
Gaskill, J. (1978). Linear Systems, Fourier Transforms, and Optics. New York: Wiley.
Mahajan, V. N. (2001). Optical Imaging and Aberrations. Bellingham: SPIE Optical Engineering Press.
Wyant, J. C. and Creath, K. (1992). Basic wavefront aberration theory for optical metrology. Applied Optics and Optical Engineering 11, 1.