| 摘要 |
An objective of great overall length having two lens groups with a positive lens power and an aperture disposed in front of or within of the first lens group. The first lens group includes a positive lens and a negative lens. The second lens group has at least four lens components with lens powers of positive, negative, positive and negative, respectively the distance between the two lens groups being greater than the focal length of the objective. Additionally, the lens components of the second lens group satisfy the following conditions: R21<f R26<f/2 -R29<f wherein R21 is the radius of curvature of the front surface of the first lens component; R26 is the radius of curvature of the back surface of the second lens component; R29 is the radius of curvature of the front surface of the fourth element lens component; and f is the focal length of the objective.
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