| 摘要 |
PURPOSE:To obtain a high variable power variation ratio of 4 by providing four lens groups which have a negative, a positive, a negative, and a positive focal length successively from a subject side, and allowing this optical system to meet specific requirements. CONSTITUTION:The 1st, the 2nd, the 3rd, and the 4th lens groups are all moved mechanically to vary the power, and a subject plane and an image plane are held at a specific distance to meet various requirements shown by inequalities I -X. In the inequalities, N1 is the refereactive index of the (d) line of the 1st lens, rIIIa and rIIIb are the radii of curvature of the image-side concave surface and image-side concave surface of the subject-side negative lens group in the 3rd lens, and NII is the mean value of the refractive index of the (d) line of the lens in the 3rd lens group; rIV1 is the radius of curvature of the 1st surface of the 4th lens group, and fs is the focal length of the whole system on the low-power side; ms is the lateral power of the low power side and m1s, m12s, and m123s are the composite lateral power values of the 1st, the 2nd, and the 1st- 3rd lens groups on the low-power side; and Xi is the extent of movement of the (i)th lens group and fBS is the back focus of the low power side.
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