Anatomy and physiology of the eye, with hints for the preservation of the eyesight (1901)
Herbert, John Frederick, 1860- · Philadelphia, Pa., The author · leaf 58
tre must necessarilyhave just twice the refracting power of one which focussessimilar rays at a point one metre off. A lens of one diopter (i. D) will focus parallel rays attwo (2, D) I metre, threefour (3.D)(4. D) etc. Therefore the higher the number of the lens in dioptersthe greater is its… … Figure ^z-A. Convex cylitidiical lens. B. Concave cylindrical lens. These lei\ses are used for the correction of astigmatism, and ditler from spherical ietises because the rays refracted through them do not focus at a poiiit, but focus as a line of light, as shown in figure. (Compare with figure…
Eye · Lenses
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