| 摘要 |
The wide angle photographic objective of the retrofocus type has the back focus of 0.9 to 1.25 times the focal length of the objective while it has the angle of field of 63 DEG and the relative aperture of F2.8. The objective consists of six lens components the first component of which is a negative meniscus, while each of the second to fourth components is a positive lens element and the fifth component is a negative concavo-concave lens element, the sixth component consisting of two lens elements cemented to each other with the cemented surfaces being convex toward the object, the sixth component having a positive refractive power as a whole. In order to compensate for the aberrations, the objective satisfies the following conditions: 0.5 ¦ fl¦ < f2 < 5.0 ¦ f1 ¦ 0.25 f < d2 0.15 f < d3 < 0.3 f 0.5 f < ¦ r8 ¦ < 2.5 f d8 + d10 < 0.2 f ¦ n6 - n 7¦ < 0.
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