|landscape lens and prisms illustrating how the glass combination works|
The achromatic lens is a simple solution to reduce chromatic aberration. Its a lens consisting of one group of two or three lens elements. An old landscape lens may consist of such a group, i.e. a biconvex crown glass element and a biconcave flint glass element. Other achromatic lenses use other variants of concave flint glass element and convex crown glass element(s).