提出了一种基于 CCD(电荷耦合器件 )模拟视频信号分析法的显微镜自动对焦改进方法。许多基于视频信号分析法的自动对焦系统仅考虑视频信号的高频分量, 忽略低频分量在对焦过程中的变化。本文对模拟视频信号进行频谱分析, 研究不同频率范围的信号对对焦评价曲线的影响, 得出适合自动调焦的粗调 /细调的频域范围, 使系统有更广调焦范围的同时保持较高精度。最终通过实验验证, 加入适当的滤波电路后调焦范围更广, 40倍物镜下显微镜自动对焦系统的有效调焦范围可达 ±500 μm。

An autofocus method based on the analog video signal of the microscope CCD (Charge Coupled Device)is presented, which can improve the autofocus range. In many autofocus modes, the high-frequency energy of the video spectrum is taken into account, while ignoring the changes of the low-frequency energy of the video spectrum in the focusing process. In this presentation, the spectrum of the analog video signal was analyzed, including the affection of the different frequency range analog signal on the focusing evaluation curves. Based on the analysis, we obtain the proper frequency range that fit the coarse/fine adjustment of the autofocus process. The resulting system has a wider focusing range while remaining the high accuracy. Experimental results show that the proper filter can extend the autofocus range.Using the 40× microscope objective, the effective autofocus range of the microscope can reach ±500 μm.