| 摘要 |
A bright telephoto lens having a small telephoto ratio and with a properly compensated secondary spectrum which would otherwise largely affect the image-forming ability of the lens. The telephoto lens has a convergent lens group on the opposite side and a divergent lens group on the image side. The convergent group includes first, second and third positive lenses and a single negative lens, the first positive lens being closest to the object and made of an optical material having a partial dispersion ratio in the range of from 1.22 to 1.29 with respect to g-line and d-line. The negative lens is disposed more closely to the image than the first positive lens. The second and third positive lenses are disposed more closely toward the image than the first positive lens and are made of an optical material of anomalous dispersion having a partial dispersion ratio in the range of from 1.22 to 1.24 with respect to g-line and d-line, and have an Abbe number nu d which ranges from 80 to 95.5. The telephoto lens satisfies the following relations: <IMAGE> (1) 23.5 < nu dn < 55.0 (2) <IMAGE> (3) where psi 1, psi 2, psi 3 are the refractive powers of the first, second and third positive lenses, respectively, nu dn is the Abbe number of the negative lens, psi p is the sum of the surface refractive powers of the three positive lenses on their image sides, and psi n is the surface refractive power of the negative lens on the image side, with psi n<0.
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