Traditional nautical-type telescopes, or refractors, use an objective lens to focus the image and an eyepiece to view it. Their main drawback is that the image suffers from chromatic aberration, because light of different colours is brought to a focus at slightly different distances from the objective lens, producing coloured fringes around the image. Isaac Newton was the first person to explain chromatic aberration in the seventeenth century but, because he thought that it could not be corrected, he produced a completely different design of telescope in which the image is formed be a parabolic mirror. Newtonian reflectors, as they are called, do not suffer from chromatic aberration.
KeywordsQuartz Europe Income Hexagonal Chlorine
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