| 摘要 |
680,185. Optical objectives. VERKAUFSAKT.-GES., H. WILD'S GEODATISCHE INSTRUMENTE. Feb. 1, 1951 [Feb. 13, 1950], No. 2571/51. Class 97 (i). A wide-angle objective particularly for photography or projection consists of six airspaced components of which the two middle ones are convergent with a diaphragm therebetween, and the two at either side thereof are divergent, the air spaces between the respective divergent components each having the form of a converging meniscus concave towards the diaphragm. Preferably the outer surfaces of the middle components are convex and are separated by an axial distance of between 0.6 F and 1.4 F, where F is the focal length of the objective, the central air-space being greater than 3 per cent F. Where the four divergent components are simple lenses the sum of their refractive indices does not reach 6.30. A nurnerical example is given of the lens shown in which the middle components are triplets, the refractive indices decreasing from element L 3 to element L 5 and from element L 8 to element L 6 . A numerical example is also given of a similar lens in which the front middle component is a doublet, i.e. the element L 5 is omitted.
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