. A treatise on diseases of the eye . :------- o 0-^^ Fig. 62. Aberration.—It is only when small pencils of light are isolated thatwe may assume that all the rays meet in their conjugate foci after refrac-tion at a spherical surface. ^Nhen a large sector of the wave passes intothe second medium the angles of incidence of the rays increase so rapidly,as the distance from the axis increases, that the more peripheral raysare refracted too much in proportion to the central rays, so that thesharpness of the focus is marred. This constitutes spherical aberration. Chromatic Aberration.—This results f
. A treatise on diseases of the eye . :------- o 0-^^ Fig. 62. Aberration.—It is only when small pencils of light are isolated thatwe may assume that all the rays meet in their conjugate foci after refrac-tion at a spherical surface. ^Nhen a large sector of the wave passes intothe second medium the angles of incidence of the rays increase so rapidly,as the distance from the axis increases, that the more peripheral raysare refracted too much in proportion to the central rays, so that thesharpness of the focus is marred. This constitutes spherical aberration. Chromatic Aberration.—This results from the fact that the variouscolors are not equally refracted. The refraction increases as the wavelength diminishes. Violet is, therefore, the color of greatest, and red isthe color of least, refraction. Lenses.—A lens is defined as a portion of refracting material boundedbv one curved and one plane surface, or by two curved surfaces. Classification.—Lenses are classified (Pig. 63) as (1) plano-convex, (2)biconvex, (3) concavo-convex and (4) convexo
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Keywords: ., bookcentury1900, bookdecade1910, booksubjecteyediseases, bookyear
