| 摘要 |
870,189. Telephoto objectives. ISCO OPTISCHE WERKE G.m.b.H. Oct. 31, 1958 [Nov. 27, 1957], No. 34975/58. Drawings to Specification. Class 97(1) A telephoto objective comprises a positive simple component at the front and a positive simple component at the rear and between these components a negative component consisting of a positive and a negative element, cemented together or in broken contact, wherein the simple component at the front and the positive element adjacent thereto each have a refractive index less than 1.60, the sum of the refractive indices in the entire objective is less than 6.80 the sum of the AbbÚ numbers is less than 175, and the rear face of the third element is concave towards the rear and is separated from the rear component by between 0À15f and 0À25f, where f is the equivalent focal length of the objective. Preferably the refractive index difference between the elements of the middle member is between 0.12 and 0.18. Optical data are given for two examples.
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