A lens is primarily defined by its focal length. Figure 4 illustrates the relationship between the focal length of the lens, field of view, sensor size, and working distance.

一个镜头的基础定义是其焦距，图4图示出镜头焦距，视野，感应器大小，和工作距离间之关系。

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Once you choose a lens whose focal length is closest to the focal length required by your imaging system, you need to adjust the working distance to get object under inspection in focus.

一旦你选择一个镜头其焦距是最接近于你成像系统所需之焦距，你需要调较工作距离去获取观察目标物的焦点。

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Focal point is, the distance between the two is the focus of the focal length.

定点是焦点，两焦点的距离是焦距。

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