| 单词 | equivalent focal length |
| 释义 | > as lemmasequivalent focal length b. Optics. equivalent focal length (see quots.). ΚΠ 1867 T. Sutton & G. Dawson Dict. Photogr. (ed. 2) 116 Suppose that a lens..when presented towards a distant object, renders the image of it a certain size upon the ground glass. Then the ‘equivalent focal length’ of that lens..is equal to the principal focal length of a single lens, having a small stop in close contact with its central portion, which gives the same sized image of that object, when taken from the same point of view. 1961 A. L. M. Sowerby Dict. Photogr. (ed. 19) 335 The focal length, or equivalent focal length, of a lens is defined as the distance from the node of emission, to the position at which the lens forms a sharp image of a distant object. < as lemmas |
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