MODIFIED TRIPLETS WITH REDUCED SECONDARY SPECTRUM

摘要

A lens, particularly usable in a printer, consists of a middle negative component surrounded by two positive doublets. Secondary spectrum is reduced by choosing refractive materials and element focal lengths to minimize the expression (Pm - P3/V3 - Vm), where P3 and V3 are the partial dispersion and Abbe number for the negative component and Pm and Vm are the mean equivalent partial dispersion and mean equivalent Abbe number for the doublets.