| 摘要 |
PURPOSE:To compensate aberrations excellently over the entire image surface and to shorten the overall length of a two-group zoom lens consisting of lens groups which have positive and negative refracting power by specifying the lens shapes of the lens groups and making at least one lens surface of the 2nd lens group aspherical in a specific shape. CONSTITUTION:A lens surface R11 is made into an aspherical surface RAS as shown by a full line so that the negative refracting power is less at the 70% position of its effective diameter than at the 50% position. Thus, three off-axis light beams Ai-Ci are reduced in divergence as compared with a spherical surface to obtain light beams Ao'-Co' shown by full lines, and the inclination of a meridional image surface is corrected, so that an image is formed while the curvature of field is compensated on the whole. Further, at least one lens surface in the 2nd lens group is made aspherical to reduce aberration variation during power variation and compensate various aberrations over the entire image surface excellently.
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