| 摘要 |
PURPOSE:To increase the magnification during close-up enlargement observation and to compensate aberrations excellently by arranging the 1st negative lens group, a diaphragm, the 2nd and the 3rd positive lens groups, the 4th group of a positive-negative cemented lens, and the 5th positive lens group in order, and allowing this lens system to meet specific requirements. CONSTITUTION:The diaphragm and the 2nd group consisting of a positive meniscus lens having the concave surface at the object side are arranged next to the 1st group of a negative lens, the 3rd group of a positive lens, the 4th group of the cemented lens of a positive and a negative lens, and the 5th group of a positive lens are further arranged, and the 3rd group and the 4th groups are extended partially to perform focusing. Further, conditional inequalities I and IIhold for the focus length f1 of the 1st group, the composite focal length f2 of the 2nd and the 5th groups, and the focal length fa of the whole system in close-up photography, and consequently close-up enlargement magnification is secured and the Petzval's sum is corrected properly, thereby correcting the inclination of image plane curvature to the plus or minus side.
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