A manual of photographic chemistry, theoretical and practical . ceding 334: OPTICS OF PHOTOGEAPHY. diagram shows this. Y represents the focus of the violet ray,Y of the yellow, and R of the red. Hence, as the chemicalaction corresponds more to the violet, the most marked actiniceffect would be produced nearly at Y. The luminous portionof the spectrum, however, is the yellow, consequently thevisual focus is at Y. Photographers have long recognized this point; and there-fore, with ordinary lenses, not corrected for actinism, rules arelaid down as to the exact distance which the sensitive platesh
A manual of photographic chemistry, theoretical and practical . ceding 334: OPTICS OF PHOTOGEAPHY. diagram shows this. Y represents the focus of the violet ray,Y of the yellow, and R of the red. Hence, as the chemicalaction corresponds more to the violet, the most marked actiniceffect would be produced nearly at Y. The luminous portionof the spectrum, however, is the yellow, consequently thevisual focus is at Y. Photographers have long recognized this point; and there-fore, with ordinary lenses, not corrected for actinism, rules arelaid down as to the exact distance which the sensitive plateshould be shifted away from the visual focus in order to ob-tain the greatest amount of distinctness of outline in the imageimpressed by chemical action. Actinic aberration is corrected by combining two lenses cutfrom varieties of glass which differ in their power of separat-ing the colored rays. These are generally the dense flint glasscontaining oxide of lead, and the light crown glass. Of thetwo lenses, the one is biconvex and the other biconcave; so —>. Fig. 28. that when fitted together they produce a compound actiniclens of a meniscus form, as shown in Fig. 28. The first lens in this figure is the flint, and the second thecrown glass. Of the two the biconvex is the most powerful,so as to overcome the other, and produce a total of refractionto the required extent. Each of the lenses is made from glassof different dispersive power to that of its coadjutor; and theeffect of passing the rays through both is, by overlapping thecolored spaces, to unite the complementary tints, and to re-form white light. Spherical or Axial Aierratio7i.—Spherical aberration isthe property possessed by lenses which are segments of spheresof refracting rays of light unequally at different parts of theirsurfaces. Fig 29 shows this in an exaggerated degree. Observe that the dotted lines which fall upon the circiirafer-ence of the lens are brought to a focus at a point nearer to thelens than tho
Size: 2805px × 891px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, bookdecade1880, bookidma, booksubjectphotography
