METHOD OF PRODUCING A LENS ELEMENT HAVING AN ACCURATELY CENTRED ASPHERICAL SURFACE FORMED BY REPLICATION, AND APPARATUS FOR CARRYING OUT THE METHOD

摘要

In the production of a lens element having on one side a replicated aspherical surface which is accurately axially aligned with a spherical or flat surface on the reverse side of the element, a mould tool (9) with a moulding surface (10) having an accurate negative profile of the required aspherical surface on the lens element and having the desired optical finish of this surface is mounted on a rotatable jig (1) and by means of adjustment screws (4 and 6) is adlusted to correct misalignment of the axis (M) of the moulding surface and the axis of rotation (J) of the jig. The misalignment is detected by directing a collimated light beam (13) onto a moulding surface so that it is reflected onto a screen (14) while the mould tool is rotated by means of the jig. A preformed glass lens substrate (15) having on one side an aspherical surface (16) of approximately the desired profile and finish and on the reverse side a spherical or flat surface (17) is then mounted on the jig with its aspherical surface facing and spaced from the moulding surface of the mould tool, and by means of further adjustment screws (7 and 8) the substrate is adjusted to correct misalignment of the axis (5) of the spherical or flat surface of the substrate and the rotational axis of the jig. This misalignment also is detected with the aid of the collimated light beam and the screen. The gap (18) between the substrate and the mould tool is then filled with a suitable light-transmissive polymeric material (19) in liquid form, which is allowed to harden and form a moulded layer bonded on one side to the substrate and presenting on the other side an aspherical surface of the required profile and optical finish, axially aligned with the spherical or flat surface of the substrate.