GB553660A - Improved wide angle lens attachments for photographic objectives - Google Patents

Abstract

553,660. Lenses. KODAK, Ltd. Aug. 14, 1942, No. 11417. Convention date, Sept. 3, 1941. [Class 97 (i)] In an attachment for use in front of a photographic objective 51 to increase the angle of the field, and comprising a negative component I, II spaced in front of a meniscus positive component III to provide an approximately afocal combination, the positive component is concave to the front and has a great axial thickness ; the thickness may be greater than one fourth the air space between the components and less than that for which the components are in marginal contact, or greater than one fifteenth the focal length of the positive component and less than two thirds the difference between the numerical values of the focal lengths of the components. The negative component may be compounded of at least one positive element and one negative element, and may have an axial thickness between 0.1 and 0.25 times the difference between the focal lengths of the two components ; the positive element I may be biconvex and have refractive index greater than 1.62, the refractive index of the negative II being less than 1.55. The component III may be a cemented doublet. The Specification contains data for three examples