An achromatic lens is a combination of concave and convex pieces of glass that focuses the different colour wavelengths in light to a single plane. ... Each type of glass disperses the colours differently — put together they counterbalance each other and produce a sharp image.

How does a doublet lens work?

The lenses are made from glasses with different refractive indices and different amounts of dispersion. Often one element is made from crown glass and the other from flint glass. ... In a hard-cemented doublet, the lenses are held together by an adhesive with mechanical strength, such as optically transparent epoxy.

What is meant by achromatic doublet?

An achromatic doublet is made from a pair of glasses, of which one is typically a concave and another is convex. The concave element of the doublet is composed of flint glass (with higher dispersion); the convex element, however, is made up of crown glass (with low dispersion).