GB660259A - Optical objectives - Google Patents

Abstract

660,259. Objectives. WILD SURVEYING INSTRUMENTS SUPPLY CO., Ltd. Feb. 6, 1948 [Aug. 23, 1947], No. 3588/48. Class 97 (i). In an objective which comprises four airseparated components of which the first component faces the object and is a simple converging lens L1, the second component is a meniscus convex towards the object, the third component is convergent and compound and has an axial thickness between 0.1 and 0.6 times the equivalent focal length of the objective and the fourth component is a divergent meniscus compound component convex towards the image, the air-space between the first and second components having the form of a diverging lens with the stronger curved surface r3 thereof on the image side, the air-space between the second and third components containing a diaphragm and having the form of a converging lens with the stronger curved surface r5 thereof on the object side and the air-space between the third and fourth components having the form of a convergent meniscus convex towards the image with the stronger curved surface r10 thereof on the image side, means are provided in the fourth component for causing the divergence of inclined rays to increase so that image distortion is reduced. Such means may comprise a cemented surface r12 which is convex towards the object, the refractive index of lens element L8 being greater than that of lens element L9. Alternatively, an air lens in the form of a plano-convex lens or a convergent meniscus convex towards the object or the image may be provided in the fourth component, the refractive index of the lens on the object side of the air lens being less than the refractive index of the lens on the image side thereof. Optical data are given for six examples.