| 摘要 |
898,745. Variable focal length systems. TAYLOR, TAYLOR & HOBSON Ltd. Sept. 29, 1958 [Oct. 2, 1957; Jan. 15, 1958], Nos. 30847/57 and 1446/58. Class 97(1). In a variable focal length objective of the kind comprising a movable convergent front member, a stationary convergent rear member and a movable divergent member therebetween, such that the ratio of the equivalent focal length of the divergent combination of the front two members to the equivalent focal length of the complete objective is constant throughout the range of variation and the virtual image of a distant object formed by this combination has a constant axial position relative to the stationary rear member, the convergent front member has several convergent components of which at least one is a doublet with a dispersive internal contact surface and at least one is a simple component, and the divergent second member has several divergent components of which at least one is a doublet with a collective internal contact surface and at least one is a simple meniscus component whose rear surface is convex to the front and has a radius of curvature not less than 0.33 f 2 and not greater than the range of axial movement of the divergent second member, where f 2 is the equivalent focal length of the second member. Optical data are given in the Specification for four examples; one example is as illustrated and is such that the front member comprises a positive doublet and a positive meniscus, the middle member comprises three negative menisci, and the fixed rear member comprises four components. In other forms, the front member comprises a front simple positive lens followed by a convergent doublet, and the rear member comprises three components only. Focusing for near objects may be effected by movement of the convergent front member independently of the second and third members. The rear member of each example may be replaced by other rear members so as to allow for different minima and maxima of equivalent focal length. By arranging the objective diaphragm at or near the front surface of the stationary rear member and using the front members with diameters larger than is necessary to accommodate the full axial beam, the relative aperture of the objective remains constant throughout the range of variation. Specification 689,206 is referred to. |
