| 摘要 |
PROBLEM TO BE SOLVED: To obtain an inverted telephoto type wide angle lens which is simple in constitution, is inexpensive, is long in back focus and has a good image-forming characteristic by constituting the lens of first group of a divergent system, a second group of a convergent system and a third group of a convergent system, successively from an object side and constituting the lens which satisfies specific conditions as a whole. SOLUTION: This wide angle lens is composed of the first group of the divergent system, the second group of the convergent system and the third group of the convergent system and is so constituted as to satisfy the following various conditions: 1.48<Na<1.52, 59<νa<72, 1.48<Nc5 or Nc7<1.51, 67<νc5 orνc7<85, 0.02<dc2/f<0.07, 0.045<dc4/f<0.065, 1.15<rc2/rc3<1.55, -0.95<rc4/rc5<-0.47, where, f: the focal length of the entire system, Na: the refractive index of the first group, Nc5, Nc7: the refractive indices of the third or fourth lens of the third group,νa: the Abbe number of the lens of the first group,νc5,νc7: the Abbe number of the third or fourth lens of the third group, dc1, dc2: the axial spacing of the respective refractive faces successively from the object side of the third group, rc1, rc2: the radii of curvature of the respective refractive faces successively from the object side of the third group.
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