Ophthalmic lenses, dioptric formulae for combined cylindrical lenses : the prism-dioptry, and other optical papers (1900)
Prentice, Charles Frederick, b. 1854 · Philadelphia : Keystone · leaf 37
some point within the focal interval F^-F-; such point being determinedwhere the vertical and horizontal displacements are alike, and the sectionT, consequently, a circle of least confusion. 32 COMPOUND LENSES. § 28. Astigmatic refraction in a lens is, however, preferably attained bycombining a… … Fig. 25.Convex Sphero-cylindrical Lens i+ s- -C:. + c^ axis 180°)—Double Form. To increase the refraction of a positive or negative spherical lens in onemeridian, we may add to it the active meridian of a cylinder bearing thesame sign; and to decrease it in the same meridian we may combine it…
Lenses
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