Ocular refraction and the shadow test . Figur 1!; the opli^ angles k 51- irregular shape spherical lens; PI. tlie straighunbroken, indicating centre where ihey inteippearance in another position. other, hold the lens in such a position before the crossed lines thatthey appear unbroken through the lens as shown by II, figure 51, anydeviation from this position will create an effect smiilar to that illus-strated by I, figure 51. Having located the centre, mark the irregu-lar lens the same as was done in figure 47, and the form for the de-sired size and shape lens can now be imposed with it
Ocular refraction and the shadow test . Figur 1!; the opli^ angles k 51- irregular shape spherical lens; PI. tlie straighunbroken, indicating centre where ihey inteippearance in another position. other, hold the lens in such a position before the crossed lines thatthey appear unbroken through the lens as shown by II, figure 51, anydeviation from this position will create an effect smiilar to that illus-strated by I, figure 51. Having located the centre, mark the irregu-lar lens the same as was done in figure 47, and the form for the de-sired size and shape lens can now be imposed with its geometric cen-tre upon the optical centre of the lens and this form outlined upon theblank, this will give a properly cent red X&m. To ascertain if any lens R E F R A C T I O X. is properly centred, proceed as above and see if the optical and geo-metrical centres correspond. Sometimes it is desired to dccoitrc alens, or to have the optical centre located in a certain position with. tres of lens identical; II. geometric cenlre purposely displaced regard to the geometric centre. I, iigure 52, shows a centred lens,II, figure 52, a decentered one marked out upon the blank. 4
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Keywords: ., bookcentury1900, bookdecade1900, bookidocularrefrac, bookyear1903
