A manual of photographic chemistry, theoretical and practical . hazy, owing to the ray Z being refracted in agreater degree than any others of those between it and the LENSES. 339 upper boundary ray O. If tlie transmitted ray Z, instead oftaking the coarse Z, went straight to 0,the intermediate raysdoing the same, then would we have a perfect single leris;but such is not the case, owing to the aberration caused bythe spherical surface of the glass. Spherical aberration, itmay here be once more remarked, is that property in a lenswhereby parallel rays falling either obliquely or axially uponits
A manual of photographic chemistry, theoretical and practical . hazy, owing to the ray Z being refracted in agreater degree than any others of those between it and the LENSES. 339 upper boundary ray O. If tlie transmitted ray Z, instead oftaking the coarse Z, went straight to 0,the intermediate raysdoing the same, then would we have a perfect single leris;but such is not the case, owing to the aberration caused bythe spherical surface of the glass. Spherical aberration, itmay here be once more remarked, is that property in a lenswhereby parallel rays falling either obliquely or axially uponits surface undergo such different degrees of refraction as pre-vent them meeting at one point. - The function of a diaphragm, as applied to a single achro-matic lens, having its flattest side next to the subject to be de-picted, is to prevent any rays from having access to the lens, butthose which shall be transmitted, both axially and obliquely,to a pictorially sharp focus. The manner in which the dia-phragm affects this is shown in Fig. 35, in which the axial. Fig, 35. rays are transmitted to a sharp focus, the oblique rays, all butthose which pass through the diaphragm, and come to a focusas shown, being debarred access to the lens by the mountingand the diaphragm. We shall hereafter speak of other functions of the dia-phragm. The subject is here introduced to show in what man-ner it becomes necessary to the correct working of a single-view lens, whether achromatized or not. Lenses are achromatized by a judicious combination of a con-cave lens formed of flint glass, with a crown glass convex, the re-spected degrees of curvature being so determined as to bringall the rays of the spectrum, at any rate the visual and moreenergetic of the chemical ones, to a focus. Were this not done,the plane at which by aid of the ground glass of the camera, 340 OPTICS OF PHOTOGRAPHY. the image was seen to be sharp would be somewhat distantfrom that plane at which the more violet rays were broug
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Keywords: ., bookcentury1800, bookdecade1880, bookidma, booksubjectphotography
