The rear group focusing based high-definition zoom lens is suitable for the applications that require small-caliber front group,high-standard close range imaging and deflected optical path.When short-range photograph is needed,the rear group focusing is able to gain better imaging quality compared with the front group focusing.When the focal distance is less than 50 mm,the minimum photographic distance can achieve 0.35 m without additional close-up lens (front group focusing lens requires close-up lens),which meets high quality imaging requirement for both short range and long range.For rear group focusing based high-definition zoom lens,there does not exist linear relationship between the object distance and the rear cut-off distance,and consequently the specific curves of focusing group movement are obviously different at different focal lengths and different object distances.In order to keep the focusing sensitivity within a reasonable range,the normal solution of linear relationship is not applicable for the displacement of rear group focusing.The design of nonlinear cam which can cover these specific curves is necessary.The principle and structure are analyzed and designed in this paper.%后组调焦高清变焦镜头适用于前端口径较小、近距离成像要求较高及光路需要偏折的场合.近摄时,后组调焦方式获得的成像质量比用前组调焦方法更好,焦距小于50 mm时,近摄距可达0.35m,不需要加近摄镜(前组调焦要加近摄镜),可以兼顾远近距离的高清成像要求.由于后组调焦高清变焦镜头物距与后截距的关系不是线性关系,调焦组的移动在不同焦距段的不同物距时对应不同的特征曲线,差异较大.为使调焦灵敏度处在一个合理区间,后组调焦位移不能采用通常使用的线性关系,需设计一条能覆盖这些特征曲线的非线性凸轮,因而根据其原理与结构进行了分析与设计.
展开▼
