| 单词 | positive eyepiece |
| 释义 | > as lemmaspositive eyepiece positive eyepiece n. Optics an eyepiece of an optical instrument consisting of two planoconvex lenses with their convex sides facing each other, so named because the image is formed in front of the lenses; cf. negative eyepiece n. at negative adj., adv.2, and int. Compounds. ΘΚΠ the world > physical sensation > sight and vision > optical instruments > lens > [noun] > eye-piece eyeglass1665 ocular1702 eyepiece1729 Ramsden1787 field glass1797 negative eyepiece1831 positive eyepiece1842 Kellner1865 orthoscopic1868 eye-point1875 comparison eyepiece1940 1842 W. T. Brande Dict. Sci., Lit. & Art 1221/1 The two lenses [of a telescope] are usually plano-convex, with the convex faces towards the object-glass... This eye-piece is usually called the negative eye-piece, from its having the image seen by the eye behind the field-glass [i.e. between the field-glass and the eye-glass]... Another modification..is called the positive eye-piece, because the image observed is before both lenses [i.e. between the field-glass and the object-glass]. 1874 Harper's Mag. Sept. 524/1 It has four positive eye-pieces, and one for collimating by means of a mercurial trough. 1958 Van Nostrand's Sci. Encycl. (ed. 3) 1018 When a positive eyepiece is used the magnifying power may be shown to be directly equal to the ratio of the focal length of the object glass of the telescope to the focal length of the eyepiece. < as lemmas |
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