Doublet (lens)

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In optics, a doublet is a type of lens made up of two simple lenses attached together. The lenses are made from glasses with different refractive indices and different amounts of dispersion. This combination produces a better image than a simple lens. Most commercial doublets are achromats, which are optimized to reduce chromatic aberration while also reducing spherical aberration and other optical aberrations.

Doublets were invented in the 17th century.

Trilobites, which are now extinct, had natural doublet lenses.