| 摘要 |
PROBLEM TO BE SOLVED: To enable a telephoto lens composed of a front group with positive refracting power and a rear group with negative refracting power to facilitate its assembly and manufacture with extremely simple constitution although the lens has a 0.76 telephoto ratio or is small in size by satisfying the telephoto lens of specific conditions. SOLUTION: The front group consists of a cemented positive lens element having two lenses which are a 1st positive biconvex lens and a 2nd negative meniscus lens which is cemented to the 1st lens and concave to an object side in order from the object side. The rear group consists of a cemented negative lens element having two lenses which are a 3rd positive lens which is biconvex and a 4th negative lens which is cemented to the 3rd lens and biconcave in order from the object side. Further, the lens system consists of the lenses in the two groups meeting the conditions shown by the inequalities. Here, (f) is the focal length, (d) is the on-axis air gap between the image plane of the 2nd lens and the object plane of the 3rd lens, (r) is a radius of curvature, (n) is a refractive index, andυis an Abbe number.
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