When the early astronomers looked at the sky through their telescopes, the images of the stars were surrounded by colored haloes caused by an optical error in the telescope, chromatic aberration. The error was so large that it severely limited their telescopes’ resolution. During the Great Plague of 1666, Isaac Newton retreated to his family home at Woolsthorpe, where he began a series of experiments on the colors of light. To investigate the problem, Newton ground and polished a triangular prism. He directed a beam of light through the prism onto a wall of his room, where the color spectrum was displayed. And when a part of this spectrum was passed through a second prism, no additional colors were created. From this, he concluded that glass in the prism did not create the colors but that white light consists of a spectrum of colors and the prism spread them out. Faced with these results, Newton decided that it was not possible to construct a telescope from lenses without color error. He concluded that the only way he could make a telescope without chromatic aberration was to use a mirror to focus starlight because all wavelengths obey the same law of reflection. The result was the Newtonian reflecting telescope. It wasn't until more than 90 years later that John Dollond devised a method for correcting chromatic aberration in glass lenses.

In this chapter, we will discuss the values and notation used to describe the colors of light. Then we will use the OSDsingletRev to demonstrate chromatic aberration and determine the nature and size of the color error in an image. Finally, we will describe how it can be corrected with a doublet design.