Aberrations are errors in an image that occur because of imperfections in the optical system. There are many different kinds of aberrations but here we will look at only two that are present in the eye.

• Spherical Aberration
  These occur because rays entering the eye closer to the center of the pupil are focused behind rays entering further away from the optical axis. The degree of variation depends on the amount of accommodation.

  
  code Spherical aberration with a general, spherical lens. Rays leaving the same point are focused at different locations, depending on their distance from the optical axis.

• Chromatic Aberration
  These occur because the eyes index of refraction is greater for shorter wavelengths than for longer wavelengths, therefore blue light rays are focused in front of red light rays.

  
  code This is an exaggeration of chromatic aberration for a general, spherical lens. Rays coming in parallel to the lens are focused at different locations, depending on their wavelengths.

These problems are often compensated for by neurological processing and present themselves only in certain situations, such as night work, where the pupil is dialated and outer parts of the eye contribute to spherical aberration.

back to main page