GB518467A - Improvements in lens systems - Google Patents

Abstract

518,467. Lenses. KODAK, Ltd. May 23, 1938, No. 15262. Convention date, May 22, 1937. [Class 97 (i)] In a photographic objective comprising a simple dispersive component 2 between a simple collective component 1 and a compound collective component 3, 4, the collective element 4 has a refractive index greater than 1.75, a dispersive index at least 15 per cent. greater than that of the dispersive elements 3, and a " high combined refractive and dispersive index" as defined in Specification 462,304, [Group XXIII]; the dispersive element 3 may have a'refractive index greater than 1.70, or greater than 1.65 and less than 1.75. The collective element 4 may, alternatively, have a refractive index greater than 1.70, and the dispersive element 3 a refractive index greater than 1.60 and and less than 1.70, and a dispersive index less than that of the element 4. The dispersive element 3 may be cemented either to the front or rear surface of the collective element 4. Glass as described in Specification 462,304, [Group XXIII], may be used ; data for two examples are set out in the Specification. According to the Specification as open to inspection under Sect. 91, the sum of the absolute values of the radii of curvature of the two surfaces of the compound component may be greater than 0.9 times the focal length of the objective, the radius of the front surface may be less than that of the rear surface, and the radius of the cemented surface may be greater than one third of the focal length. Other relations between the surfaces and spacings are also set out. This subject-matter does not appear in the Specification as accepted.