| 摘要 |
A photographic objective of continuously variable focal length, having four groups of lens members. The first group is of converging refractive power, the second and third of diverging, and the fourth of converging refractive power. Change in focal length is effected by axial displacement of the second and third groups relative to each other and to the first and fourth groups. The refractive powers of the movable second and third groups are so distributed that the variable air space between the third and fourth groups is larger in the wide angle position than in any other focal length position and is smaller by a factor of 0.3 than the shortest focal length of the objective. The fourth group contains in the front part lens members which include at least one laminated member with a cemented surface of negative refractive power, followed at a distance by a diverging meniscus whose concave surface faces rearwardly toward the image plane and whose focal length is larger by a factor of at last three and not more than five times the longest focal length of the objective.
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