从景深的基本概念出发,研究了电子目镜显微镜的景深与其物理景深和几何景深之间的关系。提出物理景深与几何景深在数学上满足“相或”而非“求和”关系的观点, 并以此推导出了电子目镜显微镜的景深满足的计算公式。设计了毛细管测量系统, 用其测量了有效数值孔径不同时电子目镜显微镜(横向放大率为20×10)的景深, 以及有效数值孔径等于显微物镜数值孔径时, 不同规格电子目镜显微镜的景深。实验测量结果与理论推导结果基本吻合, 表明电子目镜读数显微镜的景深值等于物理景深与几何景深中的较大值, 而不是两者之和。

On the basis of principle of the Depth of Field (DOF), the relationship between the DOF of microscopic system with its geometric DOF and physical DOF was researched. A new view that the relationship between the geometric DOF and the physical DOF satisfies “OR” instead of “SUM” in mathematics was proposed. Based on the view, this paper deduced the DOF formulae for the microscope equipped with an electronic ocular. To verify the derived results, a capillary measurement system was designed. With the measurement system, the DOFs for a microscope with a transversal magnification of 10×20 was measured experimentally by varying its effective numerical apertures and those for different types of microscopes were also measured when the effective numerical apertures were equal to the nominal values of the objectives. Obtained results show that the measured DOFs are in good consistent with the data calculated by the deduced formula. The theoretical analysis and measured results both indicate that the DOFs for the microscope system should equal the larger value between the physical DOF and the geometric DOF rather than the sum of the two values.