Improvements in bi-focal lenses and their manufacture, and in apparatus to be employed in the said manufacture / [Malcolm Bentzon].

  • Bentzon, Malcolm.
Date:
1906
Catalogue details

Licence: Public Domain Mark

Credit: Improvements in bi-focal lenses and their manufacture, and in apparatus to be employed in the said manufacture / [Malcolm Bentzon]. Source: Wellcome Collection.

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    Improvements in Bi-focal Lenses and their Manufacture, of production Iiitlierto introduced in which tire centering varies according to the curvatures of the lenses and the relative sizes of the two portions, and, as far as we are aware, no provision has been made for producing the optical centre, at will, in any desired position, and this is an important drawback and 5 has prevented a bi-focal lens from being properly made out of one piece of glass. According to this part of our invention, we obtain any desired position of the optical centre of a lens by the means hereinafter described. We provide a block made from metal, or other suitable material, and preferably of a size suitable for supporting holders for two lenses, and we shape the face of the i 0 block, from the centre towards either end, so as to form an angle at the mid line according to the curvature of the lens, or lenses, to be operated upon, the curvatures to be ground thereon, and the position of the optical centre desired. By calculations well understood by manufacturing opticians the correct angles for lenses of all curvatures can be easily ascertained. 15 The said angle block is provided with a hole on each angled face and in each hole a lens holder is fixed, the position of the said holes depending upon the degree of angle used and being easily found by calculation. Before the lenses are placed on the lens holders, a portion of each lens is cut off to a straight edge to permit of the two lenses being placed under one grinding tool. ?0 Although we have mentioned two faces for the said angleblock, it may also be made with three, or more, faces, having equal angles, each, face being pro¬ vided with a hole for a lens holder, the lenses, in this case, being shaped in such a way as to bring1 together the parts of the lenses to be operated upon by the tool. 25 The said angleblock is held by a chuck, or other device, in a lathe, or the like, and the glasses are cemented to the lens holders and the tool rotated against the lens, or the lens rotated against the tool; the reading portion of the lens is then ground away until the correct curvature has been arrived, at, when it will be found that the optical centre is invariably in the predetermined posi- 30 tion. . Instead of making the angleblock with flat faces, we may make it with curved faces, in which case the under sides of the lens holders are cut away to suit the curvatures of the block and the calculations will be made for tangents to the curved surface. The machine and tools hereinbefore described may be 35 used to make lenses on this plan one of the tool arms only being used. In solid bi-focal lenses, having a well defined and bright dividing line, or ridge, between the two portions, the said ridge forms a third reflecting sur¬ face, which is very irritating and injurious to1 the eye of the wearer, and, the edge of the ridge being sharp, renders the lens very liable' to be damaged, on 40 coming into contact with a hard surface. These defects it. is a further object of my invention to overcome, and this we effect by obscuring, or “ greying ’ , the said ridge, so that it does not constitute a reflecting surface, and by cham¬ fering the sharp edge of the ridge, so that the lens will not be liable to be injured on coming into contact with a hard surface. 45 Dated this 29th day of December, 1904. JOHNSONS & WILLCOX, 47, Lincolns Inn Fields, London, W.C. Agents. COMPLETE SPECIFICATION. “ Improvements in Bi-focal Lenses and their Manufacture, and in 50 Apparatus to be employed in the said Manufacture ”. We, Malcolm Bentzon, of 188, Strand, in the County of London, carrying on business as an Engineer under the style of Malcolm Bentzon & Co., and