Lens systems: aplanatic anastigmatic two and three element.

In some optical applications, such as thermal imagery, chromatic aberration, correction may not be necessary. The various forms of aplantic doublet are compared with respect to high order aberrations. A set of equations is described, which generates aplanatic anastigmatic two-element single aspheric systems with any specified lens separation and back focus and, as a corollary, three-element systems with two elements in contact. The method is applied to germanium Petzval, telephoto, and inverse telephoto systems.