The invention belongs to the technical field of optical precision measurement, relating to a method and a device for measuring the central thickness of a differential
confocal lens. The method comprises the steps of: firstly, respectively determining the positions of a vertex at the front surface and a vertex at the rear surface of a lens to be measured through a differential
confocal and fixed-focal principle and obtaining position coordinates positioned two times by a differential
confocal measuring head; and then calculating the central thickness of the lens by utilizing a
ray tracing formula. Meanwhile, an annular
pupil is introduced into a measuring
optical path to shade a paraxial
ray and form a hollow measuring
light cone, which lightens the influence of aberration on a measuring result. The device comprises a
beam splitting system, an objective lens, a differential confocal
system, a length measuring
system and a mobile guide rail; wherein the
beam splitting system, the objective lens and the lens to be measured are sequentially placed in an emergent
ray direction of a collimation
light source and the differential confocal system is placed in the reflecting direction of the
beam splitting system. By utilizing the differential confocal
light cone to accurately position the surface of the lens, the invention realizes the non-
contact high precision measurement of the central thickness of the lens.