Achromatic Doublet
(a) Chromatic aberration is caused by the dependence of a lens's index of refraction on color (wavelength). The lens is more powerful for violet (V) than for red (R), producing images with different locations and magnifications. (b) Multiple-lens systems, such as this achromatic doublet, can partially correct chromatic aberrations, but they may require lenses of different materials and add to the expense of optical systems such as cameras.
Source
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"OpenStax College, College Physics. January 6, 2013."
http://cnx.org/content/m42292/latest/?collection=col11406/1.7
OpenStax CNX
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