Abstract: In a method for measuring a reference position of a tool relative to a workpiece, the tool is fastened to a first holder of a machine tool. The workpiece is to be manufactured using the tool and is fastened to a second holder of the machine tool. The tool provides a distinguishing mark on the workpiece in a predetermined reference position of the first holder relative to the second holder. Subsequently, the distinguishing mark is detected by a sensor. Therefore, the reference position of the tool relative to the workpiece is determined from a position of the first holder relative to the second holder. The tool and the sensor are fastened in fixed, permanent positions relative to one another and relative to the first holder. The accuracy of measurement of the position of the tool depends exclusively on the accuracy of positioning of the first holder relative to the second holder.

Abstract: A method of manufacturing lens elements, in which a glass preform heated to the softening temperature and an annular metal holder (3) enclosing the glass preform are arranged between the heated moulding dies (7,9) of a mould and are moulded in a pressing step into a lens element comprising a glass lens (21) and a ring (3) enclosing the glass lens and acting as a fitting. During moulding, the ring 3 forms together with the two dies (7,9) a quasi closed moulding cavity having an annular gap (15). During moulding, the ring (3) is expanded radially and a quantity of glass is pressed.