GB435109A - Multifocal lenses - Google Patents

Abstract

435,109. Spectacle lenses. CULVER, E., 42, Coolhurst Road, Crouch End, and EMERSON, S. A., 24, Wentworth Park, Finchley, both in London. March 8, 1934, No. 7434. [Class 97 (i)] A trifocal lens is made by preparing a button by assembling, such as by fusion, pieces of glass of high and intermediate refractive indices in such a way that the pieces of intermediate index are on either side of, or partially or entirely surround the piece of high index, the button so formed being surfaced to the required countersink and then united to a blank of low refractive index having a corresponding depression curve. The button may be made by forming in a piece of glass 1 of intermediate index a hole or slot into which is fused a piece of glass 4 of high index. A portion of the button is removed by cutting, for example along the line 5, Fig. 7, and the part so removed is replaced by a piece 6, Fig. 10, having the same refractive index as the blank to which the button is to be fused. The button is fused into a depression in the blank 7, and after grinding &c. a lens as shown in Fig. 15 is obtained having a distance field 7, an intermediate field 1 and a reading field 4. By cutting along the line 13, Fig. 7, a lens is obtained in which the reading field is entirely surrounded by the intermediate field. The button may be reduced to a central strip by cutting along the lines 19, 20 so that in the finished lens the intermediate field occurs only at the sides of the reading field. In an alternative method of making the button two pieces 25, Fig. 28, of intermediate refractive index are fused to the sides of a piece 26 of high index, and pieces 27, 28 of low index are then fused to the upper and lower edges to form a circular button. Specifications 255,941, [Class 97 (i)], and 346,866 are referred to.