A doublet is a compound lens made from two elements. The elements may be cemented together (forming a cemented doublet) or separated by an air space (forming a separated doublet). The most common doublet is the achromatic lens, consisting of a crown glass and a flint glass element chosen so that the indices of refraction of two separated wavelengths (one red, one blue) are equal.
Related category OPTICS AND OPTICAL PHENOMENA
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