chromatic aberration
A defect in a lens in which the various colors
of the spectrum are not brought to the
same focus. Blue light, for example, is refracted (see refraction)
more than red light when it passes through a lens and hence comes to a focus
inside that of red light. The result is fringing
– the formation of a colored halo around the image. This problem
seriously affected the performance of refracting
telescopes for centuries and was the reason that so many refractors
were built with large focal ratios:
longer focal length lenses show less chromatic error. A better solution
came with the introduction of corrective elements, using at least two different
types of glass, into a compound lens. An achromatic
lens corrects for red and blue light, whereas an apochromatic
lens corrects for at least red, blue, and green. Reflecting
telescopes are free from this type of aberration.
Related
entry
• aberration,
optical
Related category
• OPTICS
AND OPTICAL PHENOMENA
Also on this site:
Encyclopedia
of Alternative Energy & Sustainable Living
Encyclopedia
of History
BACK TO TOP
|
