This is because an image can have a varying Blur Width (depth of field) and the subject which is to be in focus is usually in the center.

这是因为图像可能有不同的模糊边缘宽度（景深）和在该中心通常有需要聚焦的被摄物体。

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The width, height, brightness of the screen and the luminous flux, focus of the cineprojector are important factors of cinema auditorium design.

银幕的宽度、挂高、亮度，以及放映机的光通量、焦距等都是电影观众厅设计的重要因素。

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Keep your arms at shoulder width, and focus on feeling your fingertips move toward the far wall with each pulse.

双臂与肩同宽，注意体会每次蝶动时手指尖指向远方池壁滑水的感觉。

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