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首页> 外文会议>RIAO/OPTILAS 2004 >Focal length assessment by self-imaging
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Focal length assessment by self-imaging

机译：通过自我成像进行焦距评估

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摘要

Several classical and modem approaches were developed in the literature for measuring the focal length of a lens. We focus our attention on those that employ self-imaging methods. In our proposal, a collimated laser beam illuminates a test lens. After the lens, the wavefront becomes convergent or divergent according to the lens power. Attached to the lens, we place a Ronchi grating. This procedure gives rise to several classical Talbot images, although magnified due to the non-parallel illumination. Key to our presentation is the use of the property that the pitch of each self-image is directly related to the focal length of the collimating lens. To obtain the pitches, a lensless CCD camera is positioned in any two consecutive self-images planes. The respective images are captured and processed. We designed software that allows first to precisely focus each self-image plane by a best-contrast algorithm, and then takes an intensity histogram along a direction perpendicular to the grating lines. By measuring the distance between consecutive self-image planes and their pitches, the focal length is determined. This method provides a reference testing with higher setting sensitivity and an increase in the accuracy compared to previous methods. Note that the proposed method represents a practical improvement over other existing methods.
机译：在文献中开发了几种经典和现代的方法来测量透镜的焦距。我们将注意力集中在采用自我成像方法的设备上。在我们的建议中，准直的激光束照亮了测试透镜。在透镜之后，波前根据透镜的屈光力而会聚或发散。在镜头上，我们放置一个Ronchi光栅。尽管由于非平行照明而被放大，但此过程会产生一些经典的Talbot图像。我们演示的关键是利用每个自像的间距与准直透镜的焦距直接相关的特性。为了获得间距，将无镜头CCD相机放置在任意两个连续的自像平面中。捕获并处理各个图像。我们设计的软件允许首先通过最佳对比度算法精确聚焦每个自像平面，然后沿垂直于光栅线的方向拍摄强度直方图。通过测量连续的自像平面之间的距离及其间距，可以确定焦距。与以前的方法相比，此方法提供了更高的设置灵敏度和更高的准确性的参考测试。注意，所提出的方法代表了对其他现有方法的实际改进。

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