| 摘要 |
PROBLEM TO BE SOLVED: To highly accurately correct chromatic aberration and to obtain high contrast in a high spatial frequency area by specifying the ranges of the refractive indexes of four convex lenses and two concave lenses and the correction condition of axial chromatic aberration. SOLUTION: In this lens, the 1st to 4th groups are successively arranged from the object side to the image side, and the constitution of the lens is four groups and six lenses. When it is assumed that the average refractive index (with respect to line (e)) of the respective refractive indexes n1, n2, n5 and n6 and the average Abbe's number of the respective Abbe's numbersν1,ν2,ν5 andν6 of 1st, 2nd, 5th and 6th lenses having positive refractive power are respectively (n)convex and (ν)concave, the average refractive index (with respect the line (e)) of the respective refractive indexes n3 and n4 and the average Abbe's number of the respective Abbe's numbersν3 andν4 of 3rd and 4th lenses having negative refractive power are respectively (n)concave and (ν) concave; they satisfy conditions of -0.006<(n)convex-(n) concave<0.05 and 14.7<(ν)convex-(ν)concave<19.8.
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