1. Newtonians explain this by saying that the achromatic refractor's crown glass and flint glass refract light as a whole with equal intensity but disperse individual colors differently.

2. Aplanat: A system of lenses invented by Adolph Steinheil, in 1866, for use in photography, consisting of a biconvex crown-glass lens placed between two concavo-convex lenses of flint-glass.

3. The Achromatic lens consists of a double convex lens of crown glass combined with a plano-concave lens of flint glass. PHYSICS WILLIS EUGENE TOWER Achromatic lenses are used in all high-grade optical instruments such as telescopes and …