GLASS LENS HAVING REDUCED CHROMATIC ABERRATION AND REFRACTIVE INDEX GRADIENT

摘要

A glass lens having a reduced chromatic aberration and a refractive index gradient such that its refractive index is expressed by the following equation N = No (1 - ar2) WHEREIN N is the refractive index at a distance r from the central axis of the lens in a cross section perpendicular to the central axis, No is the refractive index at the central axis, and a is a positive constant; WHEREIN THE COMPOSITION OF THE GLASS LENS AT ITS CENTRAL AXIS IS 2-50MOL% OF Cs2O, 30-98 mol% of Sio2 and 0-30 mol% of B2O3 with the provisio that (SiO2 + B2O3) is 50-98 mol%, and optionally other ingredients, the concentration of cesium ions in the lens gradually decreasing from the central axis of the lens to its peripheral surface to provide said refractive index gradient, said glass lens has a diameter of 0.2 to 5 mm, the difference between the refractive index of the peripheral surface of the lens and No is at least 0.003, and ¦ DELTA P¦/P is less than 0.05.