| 摘要 |
PROBLEM TO BE SOLVED: To provide a photographic objective having a focal distance (f) of 40 to 80 mm, realizing the shortening of structural length by the reduction of the number of lenses, having a large aperture ratio more excellent than 1:2.8, and improved in image forming characteristic in a short distance to an object distance of about 0.7 m. SOLUTION: The corrected double Gaussian objective has a front group comprising three lens elements (L1, L2 and L3) having positive, positive and negative refractive power lines, a diaphragm, and a rear group including a plurality of lens elements (L4, L5 and L6) having negative, positive and positive refractive power lines. In the rear group, the lens element (L4) having negative refractive power is constituted as a meniscus lens concave to the diaphragm and having an aspherical surface, and a lens element (L7) whose both surfaces are concave and which has negative refractive power is installed behind the 2nd lens element (L6) having positive refractive power. COPYRIGHT: (C)2005,JPO&NCIPI
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