| 摘要 |
An original reading lens includes a four-group, five-element lens configuration including three positive lenses and two negative lenses, wherein the positive lens is constructed by a glass material of low dispersion, and the negative lens is constructed by a glass material of high dispersion, a partial dispersion theta gd is defined by theta gd=(ng-nd)/(nF-nc) by a refractive index nd of d line (587.56 nm), a refractive index nc of c line (656.27 nm), a refractive index nF of F line (486.13 nm), and a refractive index ng of g line (435.83 nm), a straight line connecting a coordinate point of a reference glass material K 7 , K 7 (theta gd, nu d) and a coordinate point of a reference glass material F 2 , F 2 (theta gd, nu d) on a plane with a coordinate system including the partial dispersion theta gd and an Abbe number nu d as orthogonal two axes is adopted as a reference line, and a partial dispersion deviation delta theta gd which is the deviation from the reference line of the partial dispersion theta gd of the material is positive in one or more positive lens.
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