Cemented doublet lens with an extended focal depth.

A method of designing a lens with an extended focal depth is studied. The lens is a cemented doublet composed of a birefringent lens and a conventional lens. The crystal optical axis of the birefringent lens is perpendicular to the axis of the optical system. By properly selecting the parameters of the birefringent lens and the conventional lens, we can flexibly configure an imaging system that simultaneously has a large focal depth and high resolution. We also provide a theoretical analysis which shows that the focal depth of the lens is approximately 1.5 times that of a conventional lens.