Anatomy and physiology of the eye, with hints for the preservation of the eyesight (1901)
Herbert, John Frederick, 1860- · Philadelphia, Pa., The author · leaf 56
deflection is always toward the thickest part of the lens. There are two systems for numbering lenses; one iscalled the inch system and the other the dioptric system.The diopter is based on the metric scale, and is much the 50 better and the more preferable, as it is more scientific.At the present… … Fig;nre 30.Parallel rays are brniii^ht to a focus at F, on opposite side of lens. This point is therefore called the principal focus of thelens L. The space intervening between the lens and itsprincipal focus, F, will depend upon the degree of curva- CONCAVE LENS.
Eye · Lenses
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