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a lens, consisting of three or more elements of different types of glass, that is designed to bring light of three colours to the same focal point, thus reducing its chromatic aberration
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition
© William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins
Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
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